Investment Securities - Summary of Other Than Temporary Impairment by Investment Category (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Losses Recorded in Earnings	$ (7)
Available - for - sale securities [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Losses Recorded in Earnings	(7)	(9)
Other Gains (losses)	6
Total Available for sale other-than-temporary impairment	(1)	(9)
Available - for - sale securities [Member] | Residential Non-agency Prime [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Losses Recorded in Earnings	(1)	(1)
Other Gains (losses)	1	(3)
Total Available for sale other-than-temporary impairment		(4)
Available - for - sale securities [Member] | Residential Non-agency Non-prime [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Losses Recorded in Earnings	(6)	(7)
Other Gains (losses)	5	3
Total Available for sale other-than-temporary impairment	(1)	(4)
Commercial Non-Agency Mortgage-Backed Securities [Member] | Available - for - sale securities [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Other Gains (losses)		(1)
Total Available for sale other-than-temporary impairment		(1)
Other asset-backed securities [Member] | Available - for - sale securities [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Losses Recorded in Earnings		(1)
Other Gains (losses)		$ 1