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Income Taxes - Additional Information (Detail) (USD $) | 12 Months Ended |
--- | --- | ---
Dec. 31, 2012 | Dec. 31, 2011 | Dec. 31, 2010
Operating Loss Carryforwards [Line Items] |  |  |
Loss carry-forwards exceed |  |  | $ 3,400,000,000
Percentage of payment to IRS, Tier C | 12.50% |  |
Percentage of payment to IRS, Tier D | 17.50% |  |
Unrecognized tax benefits | 96,900,000 | 96,900,000 | 23,050,000
Interest expense recognized | 0 | 0 |
Interest accrued | 0 | 0 |
Valuation allowance | 3,256,423,000 | 3,169,402,000 |
Net operating loss carryforwards exceeds | 3,400,000 |  | 3,400,000,000
Expiration period | Expiring in 2029 and will fully expire in 2034 |  |
Operating tax carryforward expiration year start | 2029 |  |
Operating tax carryforward expiration year end | 2034 |  |
U. S. federal net operating tax [Member] |  |  |
Operating Loss Carryforwards [Line Items] |  |  |
Net operating tax carryforward | 7,287,114,000 |  |
Ambac Assurance [Member] |  |  |
Operating Loss Carryforwards [Line Items] |  |  |
Potential payment to outstanding disputes | 100,000,000 |  |
Ambac [Member] |  |  |
Operating Loss Carryforwards [Line Items] |  |  |
Potential payment to outstanding disputes | $ 1,900,000 |  |

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