Cash and Cash Equivalents (Additional Information) (Detail) - USD ($)	Sep. 30, 2015	Dec. 31, 2014
Cash and Cash Equivalents [Abstract]
Deposits at the Federal Reserve Bank earning interest at the Federal Funds target rate	$ 639,000,000	$ 861,000,000
Interest-earning deposits in other financial institutions	429,000,000	440,000,000
Fair value of securities purchased under agreements to resell	219,000,000	98,000,000
Fair value of securities received as collateral that have been resold or repledged	$ 0	$ 0