Securities - Changes in Credit Loss Component of Other-than-Temporarily Impaired Debt Securities (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Unrealized Losses On Short Term And Long Term Investments [Line Items]
Credit losses at the beginning of the period		$ 1		$ 36
Reduction of credit losses previously recognized on sold securities				(4)
Reduction of credit losses previously recognized on held to maturity securities due to deconsolidation of VIE				(31)
Ending balance of credit losses		$ 1		$ 1