Quarterly report pursuant to Section 13 or 15(d)

Repurchase Agreements Schedule of Repurchase Agreements by Collateral Type (Details)

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Repurchase Agreements Schedule of Repurchase Agreements by Collateral Type (Details) (USD $)
In Thousands, unless otherwise specified
Jun. 30, 2013
Dec. 31, 2012
Assets Sold under Agreements to Repurchase [Line Items]    
Assets Sold under Agreements to Repurchase, Repurchase Liability $ 14,903,155 $ 12,624,510
Assets Sold under Agreements to Repurchase, Weighted Average Borrowing Rate, Excluding U.S. Treasuries and Interest Rate Swaps 0.72% 0.76%
Assets Sold under Agreements to Repurchase, Weighted Average Remaining Maturity, Excluding U.S. Treasuries and Interest Rate Swaps 86 85
Assets Sold under Agreements to Repurchase, Interest Rate 0.67% 0.72%
US Treasury Securities [Member]
    
Assets Sold under Agreements to Repurchase [Line Items]    
Assets Sold under Agreements to Repurchase, Repurchase Liability 1,000,000 997,500
Assets Sold under Agreements to Repurchase, Interest Rate 0.08% 0.30%
US Government Agencies Debt Securities [Member]
    
Assets Sold under Agreements to Repurchase [Line Items]    
Assets Sold under Agreements to Repurchase, Repurchase Liability 11,828,514 10,171,385
Assets Sold under Agreements to Repurchase, Interest Rate 0.46% 0.54%
Mortgage-backed Securities, Issued by Private Enterprises [Member]
    
Assets Sold under Agreements to Repurchase [Line Items]    
Assets Sold under Agreements to Repurchase, Repurchase Liability 1,421,285 1,177,675
Assets Sold under Agreements to Repurchase, Interest Rate 2.23% 2.50%
Inverse Interest-Only Securities [Member]
    
Assets Sold under Agreements to Repurchase [Line Items]    
Assets Sold under Agreements to Repurchase, Repurchase Liability 219,235 228,241
Assets Sold under Agreements to Repurchase, Interest Rate 1.07% 1.16%
Loans Held-for-sale, Mortgages [Member]
    
Assets Sold under Agreements to Repurchase [Line Items]    
Assets Sold under Agreements to Repurchase, Repurchase Liability $ 434,121 $ 49,709
Assets Sold under Agreements to Repurchase, Interest Rate 2.69% 2.46%