Securities - Additional Information (Detail) (USD $)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Investment Holdings
Trading securities	$ 347,000,000		$ 343,000,000
Securities with a fair value, pledged as collateral	10,600,000,000		11,600,000,000
Marketable Securities, Realized Loss, Other than Temporary Impairments, Amount	17,000,000
Net Unrealized Gain(Loss) on Trading Securities	$ 1,000,000	$ 2,000,000