Derivative Financial Instruments - Information about Fair Values of Derivative Instruments in Consolidated Balance Sheet (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Derivatives, Fair Value [Line Items]
Asset derivatives, Fair value	$ 440,518	$ 603,019
Liability derivatives, Fair value	285,659	384,866
Derivatives designated and qualifying as hedging instruments [Member]
Derivatives, Fair Value [Line Items]
Asset derivatives, Fair value	116,560	144,293
Liability derivatives, Fair value	11,665	3,825
Derivatives not designated and qualifying as hedging instruments [Member]
Derivatives, Fair Value [Line Items]
Asset derivatives, Fair value	323,958	458,726
Liability derivatives, Fair value	273,994	381,041
Interest rate swap agreements [Member] | Derivatives designated and qualifying as hedging instruments [Member]
Derivatives, Fair Value [Line Items]
Asset derivatives, Fair value	114,083	143,179
Liability derivatives, Fair value
Commitments to sell real estate loans [Member] | Derivatives designated and qualifying as hedging instruments [Member]
Derivatives, Fair Value [Line Items]
Asset derivatives, Fair value	2,477	1,114
Liability derivatives, Fair value	11,665	3,825
Commitments to sell real estate loans [Member] | Derivatives not designated and qualifying as hedging instruments [Member]
Derivatives, Fair Value [Line Items]
Asset derivatives, Fair value	6,880	1,982
Liability derivatives, Fair value	7,435	6,570
Mortgage-related commitments to originate real estate loans for sale [Member] | Derivatives not designated and qualifying as hedging instruments [Member]
Derivatives, Fair Value [Line Items]
Asset derivatives, Fair value	18,185	48,056
Liability derivatives, Fair value	5,110	197
Interest rate contracts [Member] | Derivatives not designated and qualifying as hedging instruments [Member]
Derivatives, Fair Value [Line Items]
Asset derivatives, Fair value	285,442	399,963
Liability derivatives, Fair value	248,311	365,616
Foreign exchange and other option and futures contracts [Member] | Derivatives not designated and qualifying as hedging instruments [Member]
Derivatives, Fair Value [Line Items]
Asset derivatives, Fair value	13,451	8,725
Liability derivatives, Fair value	$ 13,138	$ 8,658