Investment Securities AFS Gross Unrealized Losses (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2014	Dec. 31, 2013
Unrealized losses and fair value of available for sale securities , by investment category and time length
Unrealized losses on available for sale securities, less than 12 months	$ (49,774)	$ (82,852)
Unrealized losses on available for sale securities, 12 months or more	(37,529)	(25,182)
Total unrealized losses on available for sale securities	(87,303)	(108,034)
Fair value of unrealized losses on available for sale securities, less than 12 months	1,926,087	2,386,847
Fair value of unrealized losses on available for sale securities, 12 months or more	765,309	467,340
Total fair value of unrealized losses on available for sale securities	2,691,396	2,854,187
Obligations of state and political subdivisions (municipal securities) [Member]
Unrealized losses and fair value of available for sale securities , by investment category and time length
Unrealized losses on available for sale securities, less than 12 months	(620)	(1,525)
Unrealized losses on available for sale securities, 12 months or more	(8)	(8)
Total unrealized losses on available for sale securities	(628)	(1,533)
Fair value of unrealized losses on available for sale securities, less than 12 months	36,357	47,044
Fair value of unrealized losses on available for sale securities, 12 months or more	271	273
Total fair value of unrealized losses on available for sale securities	36,628	47,317
Number of available for sale securities in a continuous unrealized loss position less than twelve months	86	113
Number of available for sale securities in a continuous unrealized loss position for twelve months or more	1	1
Government-Sponsored Enterprise (GSE) [Member]
Unrealized losses and fair value of available for sale securities , by investment category and time length
Unrealized losses on available for sale securities, less than 12 months	(36,552)	(57,393)
Unrealized losses on available for sale securities, 12 months or more	(22,437)	(21,186)
Total unrealized losses on available for sale securities	(58,989)	(78,579)
Fair value of unrealized losses on available for sale securities, less than 12 months	1,439,729	1,887,784
Fair value of unrealized losses on available for sale securities, 12 months or more	555,664	421,082
Total fair value of unrealized losses on available for sale securities	1,995,393	2,308,866
Number of available for sale securities in a continuous unrealized loss position less than twelve months	86	106
Number of available for sale securities in a continuous unrealized loss position for twelve months or more	19	15
Private Label [Member]
Unrealized losses and fair value of available for sale securities , by investment category and time length
Unrealized losses on available for sale securities, less than 12 months	(17)	(37)
Unrealized losses on available for sale securities, 12 months or more	(1)	0
Total unrealized losses on available for sale securities	(18)	(37)
Fair value of unrealized losses on available for sale securities, less than 12 months	1,917	2,105
Fair value of unrealized losses on available for sale securities, 12 months or more	38	35
Total fair value of unrealized losses on available for sale securities	1,955	2,140
Number of available for sale securities in a continuous unrealized loss position less than twelve months	1	2
Number of available for sale securities in a continuous unrealized loss position for twelve months or more	2	1
GNMA commercial mortgage-related securities [Member]
Unrealized losses and fair value of available for sale securities , by investment category and time length
Unrealized losses on available for sale securities, less than 12 months	(12,541)	(23,854)
Unrealized losses on available for sale securities, 12 months or more	(15,083)	(3,988)
Total unrealized losses on available for sale securities	(27,624)	(27,842)
Fair value of unrealized losses on available for sale securities, less than 12 months	425,310	443,462
Fair value of unrealized losses on available for sale securities, 12 months or more	209,336	45,950
Total fair value of unrealized losses on available for sale securities	634,646	489,412
Number of available for sale securities in a continuous unrealized loss position less than twelve months	17	19
Number of available for sale securities in a continuous unrealized loss position for twelve months or more	7	0
Other Debt And Other Equity Securities [Member]
Unrealized losses and fair value of available for sale securities , by investment category and time length
Unrealized losses on available for sale securities, less than 12 months	(8)	(43)
Unrealized losses on available for sale securities, 12 months or more	0	0
Total unrealized losses on available for sale securities	(8)	(43)
Fair value of unrealized losses on available for sale securities, less than 12 months	1,492	6,452
Fair value of unrealized losses on available for sale securities, 12 months or more	0	0
Total fair value of unrealized losses on available for sale securities	$ 1,492	$ 6,452
Number of available for sale securities in a continuous unrealized loss position less than twelve months	3	5
Number of available for sale securities in a continuous unrealized loss position for twelve months or more	0	1