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Derivative Instruments and Hedging Activities Schedule of Derivative Instruments, Gain (Loss) in Statement of Financial Performance (Details)

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Derivative Instruments and Hedging Activities Schedule of Derivative Instruments, Gain (Loss) in Statement of Financial Performance (Details) (USD $)
In Thousands, unless otherwise specified
 3 Months Ended 9 Months Ended
Sep. 30, 2013
Sep. 30, 2012
Sep. 30, 2013
Sep. 30, 2012
Derivative Instruments, Gain (Loss) [Line Items]        
Derivative Instruments, Gain (Loss) Recognized in Income, Net $ 20,434 $ 2,850 $ 66,055 $ (13,631)
Gain (Loss) on Interest Rate Swap and Swaption Agreements (55,410) (76,472) 223,388 (153,679)
Gain (Loss) on Mortgage Loans Held-for-Sale (4,443) 613 (25,262) 592
Trading Activity, Gains and Losses, Net (34,976) (73,018) 269,428 (166,732)
Forward Contracts [Member]
        
Derivative Instruments, Gain (Loss) [Line Items]        
Derivative Instruments, Gain (Loss) Recognized in Income, Net 71,751 2,170 138,429 (22,817)
Options Held [Member]
        
Derivative Instruments, Gain (Loss) [Line Items]        
Derivative Instruments, Gain (Loss) Recognized in Income, Net (37,052) 0 15,375 0
Swap [Member]
        
Derivative Instruments, Gain (Loss) [Line Items]        
Derivative Instruments, Gain (Loss) Recognized in Income, Net 71 0 (13,986) 0
Short US Treasury Securities [Member]
        
Derivative Instruments, Gain (Loss) [Line Items]        
Derivative Instruments, Gain (Loss) Recognized in Income, Net 0 (1,768) (991) (1,768)
Interest Rate Swaption [Member]
        
Derivative Instruments, Gain (Loss) [Line Items]        
Gain (Loss) on Interest Rate Swap and Swaption Agreements 3,711 (6,270) 95,476 (30,496)
Credit Default Swap, Selling Protection [Member]
        
Derivative Instruments, Gain (Loss) [Line Items]        
Derivative Instruments, Gain (Loss) Recognized in Income, Net (30,344) (18,661) (40,206) (44,187)
Credit Default Swap, Buying Protection [Member]
        
Derivative Instruments, Gain (Loss) [Line Items]        
Gain (Loss) on Interest Rate Swap and Swaption Agreements 7,852 0 7,852 0
Interest Rate Swaps Assicated with U.S. Treasuries, TBAs and MSRs [Member]
        
Derivative Instruments, Gain (Loss) [Line Items]        
Gain (Loss) on Interest Rate Swap and Swaption Agreements (8,691) (5,428) (8,371) (12,774)
Forward Sale Commitment [Member]
        
Derivative Instruments, Gain (Loss) [Line Items]        
Gain (Loss) on Mortgage Loans Held-for-Sale     0 (26)
Interest Rate Swaps Associated with Repurchase Agreements [Member]
        
Derivative Instruments, Gain (Loss) [Line Items]        
Gain (Loss) on Interest Rate Swap and Swaption Agreements (58,282) (64,774) 128,431 (110,409)
Agency To-be-Announced Securities, Non-Risk Management [Member]
        
Derivative Instruments, Gain (Loss) [Line Items]        
Derivative Instruments, Gain (Loss) Recognized in Income, Net 10,322 0 668 0
Inverse Interest-Only Securities [Member]
        
Derivative Instruments, Gain (Loss) [Line Items]        
Derivative Instruments, Gain (Loss) Recognized in Income, Net 5,686 18,094 (33,234) 43,154
Credit Default Swap, Buying Protection [Member]
        
Derivative Instruments, Gain (Loss) [Line Items]        
Derivative Instruments, Gain (Loss) Recognized in Income, Net 0 3,015 0 11,987
Forward Purchase Commitment [Member]
        
Derivative Instruments, Gain (Loss) [Line Items]        
Gain (Loss) on Mortgage Loans Held-for-Sale $ 0 $ 604 $ (20,015) $ 604