OTTI Losses on Available for Sale Securities (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013		Mar. 31, 2012
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net, Available-for-sale Securities	$ 1		$ 2
Mortgage-backed Securities, Issued by Private Enterprises [Member]
Other than Temporary Impairment Losses, Investments, Available-for-sale Securities	0	[1]	0	[1]
Other than Temporary Impairment Losses, Investments, Portion in Other Comprehensive Income (Loss), before Tax, Including Portion Attributable to Noncontrolling Interest, Available-for-sale Securities	1		2	[2]
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net, Available-for-sale Securities	$ 1	[2]	$ 2	[2]

[1] The initial OTTI amount represents the excess of the amortized cost over the fair value of AFS debt securities. For subsequent impairments of the same security, amount includes additional declines in the fair value subsequent to the previously recorded OTTI, if applicable, until such time the security is no longer in an unrealized loss position.

[2] Includes credit-related OTTI losses of $1 million and $2 million, including $1 million and $2 million of unrealized losses reclassified from OCI, before taxes, for the three months ended March 31, 2013 and 2012, respectively.