Annual report pursuant to Section 13 and 15(d)

Income Taxes - Common Stock Information (Details)

v3.3.1.900
Income Taxes - Common Stock Information (Details) - $ / shares
 12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Dividends Payable [Line Items]      
Dividends declared per share, common stock (in dollars per share) $ 2.75 $ 2.57 $ 1.875
Dividend Declared [Member]      
Dividends Payable [Line Items]      
Dividends declared per share, common stock (in dollars per share) 2.7500 2.5700 1.8750
Dividends declared per share, preferred stock (in dollars per share) 1.5569    
Ordinary Dividends [Member]      
Dividends Payable [Line Items]      
Dividends declared per share, common stock (in dollars per share) 1.9800 1.9080 0.8085
Dividends declared per share, preferred stock (in dollars per share) 1.5569    
Qualified Dividends [Member]      
Dividends Payable [Line Items]      
Dividends declared per share, common stock (in dollars per share) 0.0534 0.9240 0.8085
Dividends declared per share, preferred stock (in dollars per share) 0.0419    
Capital Gain Distribution [Member]      
Dividends Payable [Line Items]      
Dividends declared per share, common stock (in dollars per share) 0.0000 0.0000 0.0000
Dividends declared per share, preferred stock (in dollars per share) 0.0000    
Nondividend Distribution [Member]      
Dividends Payable [Line Items]      
Dividends declared per share, common stock (in dollars per share) 0.7700 0.6620 1.0665
Dividends declared per share, preferred stock (in dollars per share) 0.0000    
Installment One [Member] | Dividend Declared [Member]      
Dividends Payable [Line Items]      
Dividends declared per share, common stock (in dollars per share) 0.6500 0.6250 0.6250
Dividends declared per share, preferred stock (in dollars per share) 0.6351    
Installment One [Member] | Ordinary Dividends [Member]      
Dividends Payable [Line Items]      
Dividends declared per share, common stock (in dollars per share) 0.4680 0.4640 0.6250
Dividends declared per share, preferred stock (in dollars per share) 0.6351    
Installment One [Member] | Qualified Dividends [Member]      
Dividends Payable [Line Items]      
Dividends declared per share, common stock (in dollars per share) 0.0126 0.2250 0.6250
Dividends declared per share, preferred stock (in dollars per share) 0.0171    
Installment One [Member] | Capital Gain Distribution [Member]      
Dividends Payable [Line Items]      
Dividends declared per share, common stock (in dollars per share) 0.0000 0.0000 0.0000
Dividends declared per share, preferred stock (in dollars per share) 0.0000    
Installment One [Member] | Nondividend Distribution [Member]      
Dividends Payable [Line Items]      
Dividends declared per share, common stock (in dollars per share) 0.1820 0.1610 0.0000
Dividends declared per share, preferred stock (in dollars per share) 0.0000    
Installment Two [Member] | Dividend Declared [Member]      
Dividends Payable [Line Items]      
Dividends declared per share, common stock (in dollars per share) 0.6750 0.6450 0.6250
Dividends declared per share, preferred stock (in dollars per share) 0.4609    
Installment Two [Member] | Ordinary Dividends [Member]      
Dividends Payable [Line Items]      
Dividends declared per share, common stock (in dollars per share) 0.4860 0.4790 0.1835
Dividends declared per share, preferred stock (in dollars per share) 0.4609    
Installment Two [Member] | Qualified Dividends [Member]      
Dividends Payable [Line Items]      
Dividends declared per share, common stock (in dollars per share) 0.0131 0.2320 0.1835
Dividends declared per share, preferred stock (in dollars per share) 0.0124    
Installment Two [Member] | Capital Gain Distribution [Member]      
Dividends Payable [Line Items]      
Dividends declared per share, common stock (in dollars per share) 0.0000 0.0000 0.0000
Dividends declared per share, preferred stock (in dollars per share) 0.0000    
Installment Two [Member] | Nondividend Distribution [Member]      
Dividends Payable [Line Items]      
Dividends declared per share, common stock (in dollars per share) 0.1890 0.1660 0.4415
Dividends declared per share, preferred stock (in dollars per share) 0.0000    
Installment Three [Member] | Dividend Declared [Member]      
Dividends Payable [Line Items]      
Dividends declared per share, common stock (in dollars per share) 0.6750 0.6500  
Dividends declared per share, preferred stock (in dollars per share) 0.4609    
Installment Three [Member] | Ordinary Dividends [Member]      
Dividends Payable [Line Items]      
Dividends declared per share, common stock (in dollars per share) 0.4860 0.4825  
Dividends declared per share, preferred stock (in dollars per share) 0.4609    
Installment Three [Member] | Qualified Dividends [Member]      
Dividends Payable [Line Items]      
Dividends declared per share, common stock (in dollars per share) 0.0131 0.2335  
Dividends declared per share, preferred stock (in dollars per share) 0.0124    
Installment Three [Member] | Capital Gain Distribution [Member]      
Dividends Payable [Line Items]      
Dividends declared per share, common stock (in dollars per share) 0.0000 0.0000  
Dividends declared per share, preferred stock (in dollars per share) 0.0000    
Installment Three [Member] | Nondividend Distribution [Member]      
Dividends Payable [Line Items]      
Dividends declared per share, common stock (in dollars per share) 0.1890 0.1675  
Dividends declared per share, preferred stock (in dollars per share) 0.0000    
Installment Four [Member] | Dividend Declared [Member]      
Dividends Payable [Line Items]      
Dividends declared per share, common stock (in dollars per share) 0.7500 0.6500 0.6250
Installment Four [Member] | Ordinary Dividends [Member]      
Dividends Payable [Line Items]      
Dividends declared per share, common stock (in dollars per share) 0.5400 0.4825 0.0000
Installment Four [Member] | Qualified Dividends [Member]      
Dividends Payable [Line Items]      
Dividends declared per share, common stock (in dollars per share) 0.0146 0.2335 0.0000
Installment Four [Member] | Capital Gain Distribution [Member]      
Dividends Payable [Line Items]      
Dividends declared per share, common stock (in dollars per share) 0.0000 0.0000 0.0000
Installment Four [Member] | Nondividend Distribution [Member]      
Dividends Payable [Line Items]      
Dividends declared per share, common stock (in dollars per share) $ 0.2100 $ 0.1675 $ 0.6250
Common Stock [Member]      
Dividends Payable [Line Items]      
Ordinary dividend income percentage 72.00%    
Cash distribution percentage treated as return of capital 28.00%    
Qualified dividend income percentage 3.00%    
Preferred Stock [Member]      
Dividends Payable [Line Items]      
Ordinary dividend income percentage 100.00%    
Cash distribution percentage treated as return of capital 0.00%    
Qualified dividend income percentage 3.00%