Securities (Amortized Cost and Estimated Fair Value of Securities Excluding Trading Securities Presented by Contractual Maturity) (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Investments, Debt and Equity Securities [Abstract]
Held to Maturity, Due in one year or less, Amortized Cost	$ 117,581
Held to Maturity, Due after one year through five years, Amortized Cost	493,142
Held to Maturity, Due after five years through ten years, Amortized Cost	145,483
Held to Maturity, Due after ten years, Amortized Cost	2,373,868
Held to Maturity, Residential mortgage-backed securities, Amortized Cost	9,674
Held to Maturity, Amortized Cost	3,139,748	2,956,381
Held to Maturity, Due in one year or less, Estimated Fair Value	119,833
Held to Maturity, Due after one year through five years, Estimated Fair Value	526,769
Held to Maturity, Due after five years through ten years, Estimated Fair Value	140,891
Held to Maturity, Due after ten years, Estimated Fair Value	2,232,550
Held to Maturity, Residential mortgage-backed securities, Estimated Fair Value	9,620
Held to Maturity, Estimated Fair Value	3,029,663	2,996,944
Available for Sale, Due in one year or less, Amortized Cost	1,529,324
Available for Sale, Due after one year through five years, Amortized Cost	1,114,932
Available for Sale, Due after five years through ten years, Amortized Cost	964,001
Available for Sale, Due after ten years, Amortized Cost	444,242
Available For Sale, Residential mortgage-backed securities, Amortized Cost	1,710,664
Available for Sale, Equity securities, Amortized Cost	35,972
Available for Sale, Amortized Cost	5,799,135	5,990,577
Available for Sale, Due in one year or less, Estimated Fair Value	1,531,389
Available for Sale, Due after one year through five years, Estimated Fair Value	1,133,225
Available for Sale, Due after five years through ten years, Estimated Fair Value	964,144
Available for Sale, Due after ten years, Estimated Fair Value	454,690
Available for Sale, Residential mortgage-backed securities, Estimated Fair Value	1,776,016
Available for Sale, Equity securities, Estimated Fair Value	35,972
Available for Sale, Estimated Fair Value	$ 5,895,436	$ 6,203,299