Quarterly report pursuant to Section 13 or 15(d)

Schedule of Repurchase Agreements by Collateral Type (Details)

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Schedule of Repurchase Agreements by Collateral Type (Details) (USD $)
In Thousands, unless otherwise specified
Sep. 30, 2014
Dec. 31, 2013
Assets Sold under Agreements to Repurchase [Line Items]    
Assets Sold under Agreements to Repurchase, Repurchase Liability $ 12,274,878 $ 12,250,450
Assets Sold under Agreements to Repurchase, Weighted Average Borrowing Rate, Excluding U.S. Treasuries and Interest Rate Swaps 0.70% 0.75%
Assets Sold under Agreements to Repurchase, Weighted Average Remaining Maturity, Excluding U.S. Treasuries and Interest Rate Swaps 100 72
Assets Sold under Agreements to Repurchase, Interest Rate 0.43% 0.69%
US Treasury Securities [Member]
    
Assets Sold under Agreements to Repurchase [Line Items]    
Assets Sold under Agreements to Repurchase, Repurchase Liability 1,986,250  
Assets Sold under Agreements to Repurchase, Interest Rate (0.97%) 0.03%
US Government Agencies Debt Securities [Member]
    
Assets Sold under Agreements to Repurchase [Line Items]    
Assets Sold under Agreements to Repurchase, Repurchase Liability 8,142,314 9,109,510
Assets Sold under Agreements to Repurchase, Interest Rate 0.41% 0.46%
Mortgage-backed Securities, Issued by Private Enterprises [Member]
    
Assets Sold under Agreements to Repurchase [Line Items]    
Assets Sold under Agreements to Repurchase, Repurchase Liability 1,987,034 1,829,709
Assets Sold under Agreements to Repurchase, Interest Rate 1.86% 2.01%
Inverse Interest-Only Securities [Member]
    
Assets Sold under Agreements to Repurchase [Line Items]    
Assets Sold under Agreements to Repurchase, Repurchase Liability 142,079 166,438
Assets Sold under Agreements to Repurchase, Interest Rate 1.00% 1.05%
Loans Held-for-sale, Mortgages [Member]
    
Assets Sold under Agreements to Repurchase [Line Items]    
Assets Sold under Agreements to Repurchase, Repurchase Liability $ 17,201 $ 147,293
Assets Sold under Agreements to Repurchase, Interest Rate 3.11% 2.85%