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Income Taxes (Narrative) (Detail) (USD $) | 9 Months Ended | 12 Months Ended
--- | --- | ---
Sep. 30, 2012 | Sep. 30, 2011 | Dec. 31, 2011
Non-Variable Interest Entities [Line Items] |  |  |
Federal statutory rate | 35.00% | 35.00% | 35.00%
Net deferred tax asset | $ 1,400,000,000 |  |
Capital losses carryforward period in years | 5 years |  |
Taxable income projections, years | 15 years |  |
Maximum taxable income projections, years | 20 years |  |
Total deferred tax assets | 1,400,000,000 |  |
Capital loss carryforward |  |  | 153,000,000
NOL carryforward |  |  | 1,300,000,000
Minimum tax credit carryforward |  |  | 22,000,000
Non Variable Interest Entities [Member] |  |  |
Non-Variable Interest Entities [Line Items] |  |  |
Net deferred tax asset | 1,446,000,000 |  | 1,745,000,000
Valuation allowance | 167,000,000 |  | 236,000,000
Valuation allowance decrease | $ 69,000,000 |  |

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