Securities - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Investment Holdings [Line Items]
Trading securities	$ 343,000,000	$ 207,000,000
Securities with a fair value, pledged as collateral	11,600,000,000	12,600,000,000
Gross realized gains on trading securities	1,000,000	2,000,000	1,000,000
Gross realized losses on trading securities			(7,000,000)
Marketable Securities, Realized Loss, Other than Temporary Impairments, Amount	74,000,000	58,000,000	19,000,000
Net Unrealized Gain(Loss) on Trading Securities	3,000,000	1,000,000	5,000,000
Available-for-sale Securities
Investment Holdings [Line Items]
Marketable Securities, Realized Loss, Other than Temporary Impairments, Amount	$ 74,000,000	$ 58,000,000	$ 19,000,000