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Derivative Instruments and Hedging Activities Schedule of Derivative Instruments in Statement of Financial Position, Fair Value (Details) (USD $)
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Mar. 31, 2012
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Dec. 31, 2011
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Derivative Financial Instruments, Assets [Member]
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| Derivatives, Fair Value [Line Items] | ||
| Derivative Asset, Fair Value, Net | $ 340,715,000 | $ 251,856,000 |
| Derivative Asset, Notional Amount | 7,013,311,000 | 4,855,985,000 |
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Derivative Financial Instruments, Liabilities [Member]
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| Derivatives, Fair Value [Line Items] | ||
| Derivative Liability, Fair Value, Net | (47,475,000) | (49,080,000) |
| Derivative Liability, Notional Amount | 9,146,450,000 | 6,814,812,000 |
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Inverse Interest-Only Securities [Member] | Derivative Financial Instruments, Assets [Member]
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| Derivatives, Fair Value [Line Items] | ||
| Derivative Asset, Fair Value, Net | 246,066,000 | 157,421,000 |
| Derivative Asset, Notional Amount | 1,131,084,000 | |
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Inverse Interest-Only Securities [Member] | Derivative Financial Instruments, Liabilities [Member]
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| Derivatives, Fair Value [Line Items] | ||
| Derivative Liability, Fair Value, Net | 0 | 0 |
| Derivative Liability, Notional Amount | 0 | |
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Interest Rate Swap [Member] | Derivative Financial Instruments, Assets [Member]
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| Derivatives, Fair Value [Line Items] | ||
| Derivative Asset, Fair Value, Net | 0 | |
| Derivative Asset, Notional Amount | 0 | |
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Interest Rate Swap [Member] | Derivative Financial Instruments, Liabilities [Member]
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| Derivatives, Fair Value [Line Items] | ||
| Derivative Liability, Fair Value, Net | (28,790,000) | |
| Derivative Liability, Notional Amount | 5,810,000,000 | |
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Credit Default Swap [Member] | Derivative Financial Instruments, Assets [Member]
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| Derivatives, Fair Value [Line Items] | ||
| Derivative Asset, Fair Value, Net | 86,136,000 | |
| Derivative Asset, Notional Amount | 544,699,000 | |
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Credit Default Swap [Member] | Derivative Financial Instruments, Liabilities [Member]
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| Derivatives, Fair Value [Line Items] | ||
| Derivative Liability, Fair Value, Net | (14,638,000) | |
| Derivative Liability, Notional Amount | 154,812,000 | |
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Interest Rate Swaption [Member] | Derivative Financial Instruments, Assets [Member]
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| Derivatives, Fair Value [Line Items] | ||
| Derivative Asset, Fair Value, Net | 5,635,000 | |
| Derivative Asset, Notional Amount | 2,900,000,000 | |
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Interest Rate Swaption [Member] | Derivative Financial Instruments, Liabilities [Member]
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| Derivatives, Fair Value [Line Items] | ||
| Derivative Liability, Fair Value, Net | 0 | |
| Derivative Liability, Notional Amount | 0 | |
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Other Contract [Member] | Derivative Financial Instruments, Assets [Member]
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| Derivatives, Fair Value [Line Items] | ||
| Derivative Asset, Fair Value, Net | 1,484,000 | 2,664,000 |
| Derivative Asset, Notional Amount | 275,000,000 | |
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Other Contract [Member] | Derivative Financial Instruments, Liabilities [Member]
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| Derivatives, Fair Value [Line Items] | ||
| Derivative Liability, Fair Value, Net | (5,652,000) | |
| Derivative Liability, Notional Amount | 850,000,000 | |
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Forward Sale Commitment [Member] | Derivative Financial Instruments, Assets [Member]
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| Derivatives, Fair Value [Line Items] | ||
| Derivative Asset, Fair Value, Net | 26,701 | 0 |
| Derivative Asset, Notional Amount | 5,202,000 | |
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Forward Sale Commitment [Member] | Derivative Financial Instruments, Liabilities [Member]
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| Derivatives, Fair Value [Line Items] | ||
| Derivative Liability, Fair Value, Net | 0 | |
| Derivative Liability, Notional Amount | $ 0 |