Investments (Unrealized Losses) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Investment securities available for sale:
Fair Value, Less than 12 months	$ 1,778,244	$ 3,104,700
Unrealized Losses, Less than 12 months	4,023	43,715
Fair Value, 12 months or more	1,090,467	56,830
Unrealized Losses, Greater than 12 months	19,288	1,105
Fair Value, Total	2,868,711	3,161,530
Unrealized Losses, Total	23,311	44,820
U. S. Treasury
Investment securities available for sale:
Fair Value, Less than 12 months	999,783	102,105
Unrealized Losses, Less than 12 months	1,420	45
Fair Value, 12 months or more	0	0
Unrealized Losses, Greater than 12 months	0	0
Fair Value, Total	999,783	102,105
Unrealized Losses, Total	1,420	45
Government Agency
Investment securities available for sale:
Fair Value, Less than 12 months	291,783	780,552
Unrealized Losses, Less than 12 months	393	761
Fair Value, 12 months or more	0	29,969
Unrealized Losses, Greater than 12 months	0	31
Fair Value, Total	291,783	810,521
Unrealized Losses, Total	393	792
Mortgage Backed Securities, Other [Member]
Investment securities available for sale:
Fair Value, Less than 12 months	486,678	2,221,213
Unrealized Losses, Less than 12 months	2,210	42,876
Fair Value, 12 months or more	1,090,467	26,861
Unrealized Losses, Greater than 12 months	19,288	1,074
Fair Value, Total	1,577,145	2,248,074
Unrealized Losses, Total	21,498	43,950
Other Debt Obligations
Investment securities available for sale:
Fair Value, Less than 12 months		830
Unrealized Losses, Less than 12 months		33
Fair Value, 12 months or more		0
Unrealized Losses, Greater than 12 months		0
Fair Value, Total		830
Unrealized Losses, Total	0	33
State, County and Municipal
Investment securities available for sale:
Unrealized Losses, Total	$ 0	$ 0