Securities (Year End Securities Held to Maturity and Available for Sale) (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Schedule of Available-for-Sale Securities [Line Items]
Held to Maturity, Amortized Cost	$ 3,139,748	$ 2,956,381
Held to Maturity, Gross Unrealized Gains	27,919	45,556
Held to Maturity, Gross Unrealized Losses	138,004	4,993
Held to Maturity, Estimated Fair Value	3,029,663	2,996,944
Available for Sale, Amortized Cost	5,799,135	5,990,577
Available for Sale, Gross Unrealized Gains	105,276	212,747
Available for Sale, Gross Unrealized Losses	8,975	25
Available for Sale, Estimated Fair Value	5,895,436	6,203,299
US Treasury [Member]
Schedule of Available-for-Sale Securities [Line Items]
Held to Maturity, Amortized Cost	248,592	248,188
Held to Maturity, Gross Unrealized Gains	20,139	29,859
Held to Maturity, Estimated Fair Value	268,731	278,047
Available for Sale, Amortized Cost	2,522,159	3,020,115
Available for Sale, Gross Unrealized Gains	18,395	37,806
Available for Sale, Estimated Fair Value	2,540,554	3,057,921
Residential Mortgage Backed Securities [Member]
Schedule of Available-for-Sale Securities [Line Items]
Held to Maturity, Amortized Cost	9,674	10,725
Held to Maturity, Gross Unrealized Gains	89	300
Held to Maturity, Gross Unrealized Losses	143	0
Held to Maturity, Estimated Fair Value	9,620	11,025
Available for Sale, Amortized Cost	1,710,664	2,382,514
Available for Sale, Gross Unrealized Gains	66,791	135,514
Available for Sale, Gross Unrealized Losses	1,439	25
Available for Sale, Estimated Fair Value	1,776,016	2,518,003
US Government Corporations and Agencies Securities [Member]
Schedule of Available-for-Sale Securities [Line Items]
Available for Sale, Amortized Cost	54,024	0
Available for Sale, Gross Unrealized Losses	44	0
Available for Sale, Estimated Fair Value	53,980	0
States and Political Subdivisions [Member]
Schedule of Available-for-Sale Securities [Line Items]
Held to Maturity, Amortized Cost	2,880,482	2,696,468
Held to Maturity, Gross Unrealized Gains	7,691	15,397
Held to Maturity, Gross Unrealized Losses	137,861	4,993
Held to Maturity, Estimated Fair Value	2,750,312	2,706,872
Available for Sale, Amortized Cost	1,476,316	552,056
Available for Sale, Gross Unrealized Gains	20,090	39,427
Available for Sale, Gross Unrealized Losses	7,492	0
Available for Sale, Estimated Fair Value	1,488,914	591,483
Other [Member]
Schedule of Available-for-Sale Securities [Line Items]
Held to Maturity, Amortized Cost	1,000	1,000
Held to Maturity, Estimated Fair Value	1,000	1,000
Available for Sale, Amortized Cost	35,972	35,892
Available for Sale, Estimated Fair Value	$ 35,972	$ 35,892