Securities (Details 2) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Expected remaining maturities of debt securities available-for-sale, fair value
Fair Value	$ 7,738,051	$ 9,205,989
Total debt securities
Expected remaining maturities of debt securities available-for-sale, fair value
Securities available-for-sale, One year or less fair value	1,194,806
Securities available-for-sale, Over 1 year through 5 years, fair value	5,997,284
Securities available-for-sale, Over 5 years through 10 years, fair value	519,408
Securities available-for-sale, Over 10 years, fair value	23,524
Fair Value	7,735,022	9,204,288
Expected remaining maturities of debt securities available-for-sale, amortized cost
Securities available-for-sale, One year or less, amortized cost	1,190,413
Securities available-for-sale, Over 1 year through 5 years, amortized cost	5,906,598
Securities available-for-sale, Over 5 years through 10 years, amortized cost	489,221
Securities available-for-sale, Over 10 years, amortized cost	23,920
Total of debt securities available-for-sale, amortized cost	7,610,152
Expected remaining maturities of debt securities held-to-maturity, amortized cost
Securities held-to-maturity, Over 1 year through 5 years, amortized cost	171,235
Securities held-to-maturity, Over 5 years through 10 years, amortized cost	1,052,762
Securities held-to-maturity, Over 10 years, amortized cost	176,893
Total of debt securities held-to-maturity, amortized cost	1,400,890
U.S. Treasury
Expected remaining maturities of debt securities available-for-sale, fair value
Securities available-for-sale, One year or less fair value	3,021
Securities available-for-sale, Over 1 year through 5 years, fair value	27,349
Fair Value	30,370	20,397
Federal agency - Debt
Expected remaining maturities of debt securities available-for-sale, fair value
Securities available-for-sale, One year or less fair value	906,857
Securities available-for-sale, Over 1 year through 5 years, fair value	207,746
Fair Value	1,114,603	2,349,202
Expected remaining maturities of debt securities held-to-maturity, amortized cost
Securities held-to-maturity, Over 10 years, amortized cost	95,935
Total of debt securities held-to-maturity, amortized cost	95,935
Federal agency - MBS
Expected remaining maturities of debt securities available-for-sale, fair value
Securities available-for-sale, One year or less fair value	16
Securities available-for-sale, Over 1 year through 5 years, fair value	434,041
Securities available-for-sale, Over 5 years through 10 years, fair value	211,423
Fair Value	645,480	693,032
Expected remaining maturities of debt securities held-to-maturity, amortized cost
Securities held-to-maturity, Over 1 year through 5 years, amortized cost	2,438
Securities held-to-maturity, Over 5 years through 10 years, amortized cost	303,443
Total of debt securities held-to-maturity, amortized cost	305,881
CMOs - Federal agency
Expected remaining maturities of debt securities available-for-sale, fair value
Securities available-for-sale, One year or less fair value	174,283
Securities available-for-sale, Over 1 year through 5 years, fair value	4,750,547
Securities available-for-sale, Over 5 years through 10 years, fair value	214,401
Fair Value	5,139,231	5,318,253
Expected remaining maturities of debt securities held-to-maturity, amortized cost
Securities held-to-maturity, Over 1 year through 5 years, amortized cost	155,414
Securities held-to-maturity, Over 5 years through 10 years, amortized cost	585,593
Total of debt securities held-to-maturity, amortized cost	741,007
CMOs - Non-agency
Expected remaining maturities of debt securities available-for-sale, fair value
Securities available-for-sale, One year or less fair value	6,460
Securities available-for-sale, Over 1 year through 5 years, fair value	20,738
Securities available-for-sale, Over 5 years through 10 years, fair value	23,578
Fair Value	50,776	61,513
State and municipal
Expected remaining maturities of debt securities available-for-sale, fair value
Securities available-for-sale, One year or less fair value	91,153
Securities available-for-sale, Over 1 year through 5 years, fair value	260,487
Securities available-for-sale, Over 5 years through 10 years, fair value	70,006
Securities available-for-sale, Over 10 years, fair value	23,524
Fair Value	445,170	454,474
Expected remaining maturities of debt securities held-to-maturity, amortized cost
Securities held-to-maturity, Over 1 year through 5 years, amortized cost	13,383
Securities held-to-maturity, Over 5 years through 10 years, amortized cost	163,726
Securities held-to-maturity, Over 10 years, amortized cost	80,958
Total of debt securities held-to-maturity, amortized cost	258,067
Other debt securities
Expected remaining maturities of debt securities available-for-sale, fair value
Securities available-for-sale, One year or less fair value	13,016
Securities available-for-sale, Over 1 year through 5 years, fair value	296,376
Fair Value	$ 309,392	$ 307,417