Securities - Additional Information (Detail) (USD $)	3 Months Ended			9 Months Ended		12 Months Ended
	Sep. 30, 2013 security	Mar. 31, 2013 security	Sep. 30, 2012	Sep. 30, 2013 security	Sep. 30, 2012	Dec. 31, 2012 security
Schedule of Available-for-sale Securities [Line Items]
Securities held-to-maturity	$ 1,433,000,000			$ 1,433,000,000		$ 1,620,000,000
Temporary impairment losses recognized credit loss	0		0	0	0
Other-than-temporary securities accumulated impairment	112,000,000			112,000,000
Non-credit component unrealized loss amounts recognized						0
Assets backed securities in available for sale portfolio	24			24		27
Assets backed securities wrapped by monoline insurance company	8			8		8
Value of asset backed securites backed by insurance company	333,000,000			333,000,000		343,000,000
Fair value of asset backed securities	470,000,000			470,000,000		557,000,000
Available-for-sale securities, accumulated unrecognized holding loss	42,000,000			42,000,000		69,000,000
Fair value of financial guarantee	100,000,000			100,000,000		110,000,000
Security wrapped by below investment grade monoline insurance was deemed to be other-than-temporarily impaired	0			0		0
Assets backed securities in held for sale portfolio		6
Sold security at carrying value		71,000,000
Gross realized gains on HTM securities		8,000,000
Asset backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities held-to-maturity	208,000,000			208,000,000
Federal Home Loan Bank [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments in stock were included in other assets	139,000,000			139,000,000		143,000,000
Federal Reserve Bank [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments in stock were included in other assets	$ 482,000,000			$ 482,000,000		$ 483,000,000