Securities - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012 security	Dec. 31, 2011 security	Dec. 31, 2010
Schedule of Available-for-sale Securities [Line Items]
Percentage of debt securities issued by US Treasury, US Government Agencies and government sponsored entities	90.00%	84.00%
Temporary impairment losses recognized credit loss	$ 0	$ 0
Non-credit component unrealized loss amounts recognized	0	0
Other than temporary impairment, credit losses on debt securities held			79,000,000
Assets backed securities in available for sale portfolio	27	45
Assets backed securities wrapped by monoline insurance company	8	9
Value of Asset Backed Securities Backed by Insurance Company	343,000,000	349,000,000
Fair value of Assets Backed Securities	557,000,000	818,000,000
Unrealized Losses on Assets backed securities, Gross	69,000,000	121,000,000
Fair Value of Financial Guarantee from Insurance Company for the purpose of evaluating other then temporary Impairment	110,000,000	154,000,000
Security wrapped by below investment grade monoline insurance was deemed to be other-than-temporarily impaired		1
Maximum aggregate fair value of other than temporary impaired monoline wrapped securities (less than $1 million)		1,000,000
Federal Home Loan Bank [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments in stock were included in other assets	143,000,000	133,000,000
Federal Reserve Bank [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments in stock were included in other assets	$ 483,000,000	$ 483,000,000