Securities - Additional Information (Detail) (USD $)	3 Months Ended
	Mar. 31, 2013 security	Mar. 31, 2012	Dec. 31, 2012 security
Schedule of Available-for-sale Securities [Line Items]
Held-to-maturity Securities, Sold Security, at Carrying Value	$ 71,000,000
Percentage of debt securities issued by US Treasury, US Government Agencies and government sponsored entities	89.00%		90.00%
Temporary impairment losses recognized credit loss	0	0
Non-credit component unrealized loss amounts recognized	0	0
Assets backed securities in available for sale portfolio	27		27
Assets backed securities wrapped by monoline insurance company	8		8
Value of Asset Backed Securities Backed by Insurance Company	339,000,000		343,000,000
Fair value of Assets Backed Securities	526,000,000		557,000,000
Unrealized Losses on Assets backed securities, Gross	61,000,000		69,000,000
Fair Value of Financial Guarantee from Insurance Company for the purpose of evaluating other then temporary Impairment	110,000,000		110,000,000
Security wrapped by below investment grade monoline insurance was deemed to be other-than-temporarily impaired	0		0
Federal Home Loan Bank [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments in stock were included in other assets	143,000,000
Federal Reserve Bank [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments in stock were included in other assets			$ 483,000,000