Securities (Details 2) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Expected remaining maturities of debt securities available-for-sale, fair value
Fair Value	$ 6,838,710	$ 7,571,901
Total debt securities
Expected remaining maturities of debt securities available-for-sale, fair value
Securities available-for-sale, One year or less fair value	1,104,455
Securities available-for-sale, Over 1 year through 5 years, fair value	5,079,693
Securities available-for-sale, Over 5 years through 10 years, fair value	602,468
Securities available-for-sale, Over 10 years, fair value	50,944
Fair Value	6,837,560	7,570,674
Expected remaining maturities of debt securities available-for-sale, amortized cost
Securities available-for-sale, One year or less, amortized cost	1,099,279
Securities available-for-sale, Over 1 year through 5 years, amortized cost	4,965,611
Securities available-for-sale, Over 5 years through 10 years, amortized cost	583,091
Securities available-for-sale, Over 10 years, amortized cost	50,848
Total of debt securities available-for-sale, amortized cost	6,698,829
Expected remaining maturities of debt securities held-to-maturity, amortized cost
Securities held-to-maturity, One year or less, amortized cost	10,950
Securities held-to-maturity, Over 1 year through 5 years, amortized cost	87,301
Securities held-to-maturity, Over 5 years through 10 years, amortized cost	798,406
Securities held-to-maturity, Over 10 years, amortized cost	99,956
Total of debt securities held-to-maturity, amortized cost	996,613
U.S. Treasury
Expected remaining maturities of debt securities available-for-sale, fair value
Securities available-for-sale, One year or less fair value	10,013
Securities available-for-sale, Over 1 year through 5 years, fair value	9,189
Fair Value	19,202	19,182
Federal agency - Debt
Expected remaining maturities of debt securities available-for-sale, fair value
Securities available-for-sale, One year or less fair value	847,374
Securities available-for-sale, Over 1 year through 5 years, fair value	203,974
Fair Value	1,051,348	1,973,862
Expected remaining maturities of debt securities held-to-maturity, amortized cost
Securities held-to-maturity, One year or less, amortized cost	10,950
Securities held-to-maturity, Over 1 year through 5 years, amortized cost	33,669
Securities held-to-maturity, Over 10 years, amortized cost	59,649
Total of debt securities held-to-maturity, amortized cost	104,268
Federal agency - MBS
Expected remaining maturities of debt securities available-for-sale, fair value
Securities available-for-sale, One year or less fair value	14
Securities available-for-sale, Over 1 year through 5 years, fair value	447,143
Securities available-for-sale, Over 5 years through 10 years, fair value	273,433
Fair Value	720,590	681,044
Expected remaining maturities of debt securities held-to-maturity, amortized cost
Securities held-to-maturity, Over 5 years through 10 years, amortized cost	173,380
Total of debt securities held-to-maturity, amortized cost	173,380
CMOs - Federal agency
Expected remaining maturities of debt securities available-for-sale, fair value
Securities available-for-sale, One year or less fair value	181,389
Securities available-for-sale, Over 1 year through 5 years, fair value	4,040,298
Securities available-for-sale, Over 5 years through 10 years, fair value	178,631
Fair Value	4,400,318	4,326,907
Expected remaining maturities of debt securities held-to-maturity, amortized cost
Securities held-to-maturity, Over 1 year through 5 years, amortized cost	45,373
Securities held-to-maturity, Over 5 years through 10 years, amortized cost	545,558
Total of debt securities held-to-maturity, amortized cost	590,931
CMOs - Non-agency
Expected remaining maturities of debt securities available-for-sale, fair value
Securities available-for-sale, One year or less fair value	8,286
Securities available-for-sale, Over 1 year through 5 years, fair value	33,100
Securities available-for-sale, Over 5 years through 10 years, fair value	27,201
Fair Value	68,587	69,001
State and municipal
Expected remaining maturities of debt securities available-for-sale, fair value
Securities available-for-sale, One year or less fair value	53,996
Securities available-for-sale, Over 1 year through 5 years, fair value	209,947
Securities available-for-sale, Over 5 years through 10 years, fair value	80,836
Securities available-for-sale, Over 10 years, fair value	50,944
Fair Value	395,723	401,604
Expected remaining maturities of debt securities held-to-maturity, amortized cost
Securities held-to-maturity, Over 1 year through 5 years, amortized cost	8,259
Securities held-to-maturity, Over 5 years through 10 years, amortized cost	79,468
Securities held-to-maturity, Over 10 years, amortized cost	40,307
Total of debt securities held-to-maturity, amortized cost	128,034
Other debt securities
Expected remaining maturities of debt securities available-for-sale, fair value
Securities available-for-sale, One year or less fair value	3,383
Securities available-for-sale, Over 1 year through 5 years, fair value	136,042
Securities available-for-sale, Over 5 years through 10 years, fair value	42,367
Fair Value	$ 181,792	$ 99,074