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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 |
12 Months Ended | ||
|---|---|---|---|
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Dec. 31, 2012
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Dec. 31, 2011
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Dec. 31, 2010
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| Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items] | |||
| Balance at beginning of year | $ 127 | $ 96 | $ 60 |
| Credit losses recognized into current year earnings on debt securities for which an other-than-temporary impairment was not previously recognized | 6 | 6 | 7 |
| Credit losses recognized into current year earnings on debt securities for which an other-than-temporary impairment was previously recognized | 26 | 25 | 29 |
| Balance at end of year | $ 159 | $ 127 | $ 96 |