Investments (Unrealized Losses) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Investment securities available for sale:
Fair Value, Less than 12 months	$ 3,114,052	$ 3,104,700
Unrealized Losses, Less than 12 months	33,609	43,715
Fair Value, 12 months or more	23,622	56,830
Unrealized Losses, 12 months or more	808	1,105
Fair Value, Total	3,137,674	3,161,530
Unrealized Losses, Total	34,417	44,820
U. S. Treasury
Investment securities available for sale:
Fair Value, Less than 12 months	699,985	102,105
Unrealized Losses, Less than 12 months	1,874	45
Fair Value, 12 months or more	0	0
Unrealized Losses, 12 months or more	0	0
Fair Value, Total	699,985	102,105
Unrealized Losses, Total	1,874	45
Government Agency
Investment securities available for sale:
Fair Value, Less than 12 months	400,423	780,552
Unrealized Losses, Less than 12 months	879	761
Fair Value, 12 months or more	0	29,969
Unrealized Losses, 12 months or more	0	31
Fair Value, Total	400,423	810,521
Unrealized Losses, Total	879	792
Mortgage Backed Securities, Other [Member]
Investment securities available for sale:
Fair Value, Less than 12 months	2,012,814	2,221,213
Unrealized Losses, Less than 12 months	30,816	42,876
Fair Value, 12 months or more	23,622	26,861
Unrealized Losses, 12 months or more	808	1,074
Fair Value, Total	2,036,436	2,248,074
Unrealized Losses, Total	31,624	43,950
Other Debt Obligations
Investment securities available for sale:
Fair Value, Less than 12 months	830	830
Unrealized Losses, Less than 12 months	40	33
Fair Value, 12 months or more	0	0
Unrealized Losses, 12 months or more	0	0
Fair Value, Total	830	830
Unrealized Losses, Total	40	33
State, County and Municipal
Investment securities available for sale:
Unrealized Losses, Total	$ 0	$ 0