Cash and Cash Equivalents (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015		Dec. 31, 2014		Mar. 31, 2014	Dec. 31, 2013
Cash and Cash Equivalents [Abstract]
Cash and due from banks	$ 1,066,854	[1]	$ 1,694,329	[1]
Securities purchased under agreements to resell	236,027	[2]	95,611	[2]
Other short-term investment securities	5,122		6,122
Total cash and cash equivalents	$ 1,308,003		$ 1,796,062		$ 3,862,464	$ 1,538,779

[1] At March 31, 2015 and December 31, 2014, $236 million and $861 million, respectively, of our cash and due from banks was deposited at the Federal Reserve Bank and was earning interest at the Federal Funds target rate, and interest-earning deposits in other financial institutions were $460 million and $440 million, respectively.

[2] At March 31, 2015 and December 31, 2014, securities purchased under agreements to resell were collateralized by U.S. Treasury securities and U.S. agency securities with aggregate fair values of $244 million and $98 million, respectively. None of these securities received as collateral were sold or pledged as of March 31, 2015 or December 31, 2014.