Securities - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Investment Holdings [Line Items]
OTTI losses (less than $1 million on 2011 and 2010)	$ 0	$ 1	$ 1
Recognized recovery of OTTI losses			4
Available-for-sale investments	80	188
Asset-backed securities [Member] \| Fitch, AAA Rating [Member]
Investment Holdings [Line Items]
Asset-backed securities rated "AAA"	80.00%	91.00%
Available-for-sale investments	$ 14	$ 27
Corporate debt securities \| Fitch, A- Rating [Member]
Investment Holdings [Line Items]
In continuing operation, corporate debt securities rating A- or better		90.00%
In discontinuous operations, corporate debt securities rating A- or better	86.00%	88.00%

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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+ Details

- Definition

Before tax amount of other than temporary impairment (OTTI) on a debt security, categorized as available-for-sale, recognized in other comprehensive income (loss).

+ References+ Details

- Definition

The amount of other than temporary impairment losses on investments in debt and equity securities categorized as Available-for-sale which have been recognized in earnings during the period. Such impairment losses consist of other than temporary impairments (OTTI) on equity securities, credit losses on investments in debt securities, and when the entity intends to sell an impaired debt security or it is more likely than not that the entity will be required to sell the impaired debt security before recovery of its amortized cost basis.

+ References+ Details