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Roll Forward 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 | |
|---|---|---|
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Mar. 31, 2013
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Mar. 31, 2012
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| Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items] | ||
| Balance at beginning of period | $ 159 | $ 127 |
| Credit losses recognized into current period earnings on debt securities for which an other-than-temporary impairment was not previously recognized | 1 | |
| Credit losses recognized into current period earnings on debt securities for which an other-than-temporary impairment was previously recognized | 4 | 17 |
| Balance at end of period | $ 163 | $ 145 |