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Rollforward Amount of Credit Losses Recognized in Earnings for OTTI Securities Held by Company for Portion of Impairment Recognized in Other Comprehensive Income (Detail) (USD $)
In Millions, unless otherwise specified |
3 Months Ended | 9 Months Ended | ||
|---|---|---|---|---|
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Sep. 30, 2012
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Sep. 30, 2011
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Sep. 30, 2012
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Sep. 30, 2011
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| Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items] | ||||
| Balance at beginning of period | $ 152 | $ 105 | $ 127 | $ 96 |
| Credit losses recognized into current period earnings on debt securities for which an other-than-temporary impairment was not previously recognized | 1 | 2 | 6 | 4 |
| Credit losses recognized into current period earnings on debt securities for which an other-than-temporary impairment was previously recognized | 2 | 11 | 22 | 18 |
| Balance at end of period | $ 155 | $ 118 | $ 155 | $ 118 |