Quarterly report pursuant to Section 13 or 15(d)

Derivative Instruments and Hedging Activities Schedule of Total Return Swaps (Details)

v3.4.0.3
Derivative Instruments and Hedging Activities Schedule of Total Return Swaps (Details) - USD ($)
$ in Thousands
Mar. 31, 2016
Dec. 31, 2015
Mar. 31, 2015
Dec. 31, 2014
Derivative [Line Items]        
Derivative, Notional Amount $ (26,390,596) $ (21,998,381) $ (33,709,043) $ (48,115,523)
Total Return Swap [Member]        
Derivative [Line Items]        
Derivative, Notional Amount (868,145) (889,418) $ (877,529) $ (598,459)
Derivative, Fair Value, Net (7,120) 1,645    
Derivative, Cost 1,383 1,383    
Derivative, Unrealized Gains (Losses) (8,503) 262    
Maturity Date, 1/12/2043 [Member] | Total Return Swap [Member]        
Derivative [Line Items]        
Derivative, Notional Amount (361,370) (369,639)    
Derivative, Fair Value, Net (2,494) 456    
Derivative, Cost 866 866    
Derivative, Unrealized Gains (Losses) (3,360) (410)    
Maturity Date, 1/12/2044 [Member] | Total Return Swap [Member]        
Derivative [Line Items]        
Derivative, Notional Amount (317,908) (325,003)    
Derivative, Fair Value, Net (2,045) 350    
Derivative, Cost 1,679 1,679    
Derivative, Unrealized Gains (Losses) (3,724) (1,329)    
Maturity Date, 1/12/2045 [Member] | Total Return Swap [Member]        
Derivative [Line Items]        
Derivative, Notional Amount (188,867) (194,776)    
Derivative, Fair Value, Net (2,581) 839    
Derivative, Cost (1,162) 1,162    
Derivative, Unrealized Gains (Losses) (1,419) 2,001    
Derivative Financial Instruments, Assets [Member]        
Derivative [Line Items]        
Derivative, Notional Amount (17,869,498) (21,735,997)    
Derivative, Fair Value, Net 197,847 271,509    
Derivative Financial Instruments, Assets [Member] | Total Return Swap [Member]        
Derivative [Line Items]        
Derivative, Notional Amount 0 (889,418)    
Derivative, Fair Value, Net $ 0 $ 1,645