Securities - Changes in Credit Loss Component of Other-than-Temporarily Impaired Debt Securities (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward]
Credit losses at the beginning of the period	$ 0	$ 36
Reduction of credit losses previously recognized on sold securities	0	(5)
Reduction of credit losses previously recognized on held to maturity securities due to deconsolidation of VIE	0	(31)
Ending balance of credit losses	$ 0	$ 0