Securities (Details 2) (USD $)	Dec. 31, 2014	Dec. 31, 2013
Expected remaining maturities of debt securities available-for-sale, fair value
Fair Value	$ 5,882,983,000	$ 6,241,117,000
Expected remaining maturities of debt securities held-to-maturity, amortized cost
Total of debt securities held-to-maturity, amortized cost	3,427,031,000	2,957,843,000
Securities pledged to secure trust funds, public deposits, or for other purposes required or permitted by law	1,780,000,000
Pledged Assets Separately Reported, Securities Pledged as Collateral, at Fair Value	535,900,000
Total debt securities
Expected remaining maturities of debt securities available-for-sale, fair value
Securities available-for-sale, One year or less, fair value	656,183,000
Securities available-for-sale, Over 1 year through 5 years, fair value	5,138,801,000
Securities available-for-sale, Over 5 years through 10 years, fair value	81,505,000
Securities available-for-sale, Over 10 years, fair value	3,348,000
Fair Value	5,879,837,000	6,232,674,000
Expected remaining maturities of debt securities available-for-sale, amortized cost
Securities available-for-sale, One year or less, amortized cost	653,712,000
Securities available-for-sale, Over 1 year through 5 years, amortized cost	5,154,605,000
Securities available-for-sale, Over 5 years through 10 years, amortized cost	81,284,000
Securities available-for-sale, Over 10 years, amortized cost	3,400,000
Total of debt securities available-for-sale, amortized cost	5,893,001,000
Expected remaining maturities of debt securities held-to-maturity, amortized cost
Securities held-to-maturity, Over 1 year through 5 years, amortized cost	1,072,632,000
Securities held-to-maturity, Over 5 years through 10 years, amortized cost	2,098,697,000
Securities held-to-maturity, Over 10 years, amortized cost	255,702,000
Total of debt securities held-to-maturity, amortized cost	3,427,031,000
U.S. Treasury
Expected remaining maturities of debt securities available-for-sale, fair value
Securities available-for-sale, One year or less, fair value	91,106,000
Securities available-for-sale, Over 1 year through 5 years, fair value	25,820,000
Fair Value	116,926,000	35,335,000
Federal agency - Debt
Expected remaining maturities of debt securities available-for-sale, fair value
Securities available-for-sale, One year or less, fair value	177,218,000
Securities available-for-sale, Over 1 year through 5 years, fair value	1,221,363,000
Fair Value	1,398,581,000	1,410,536,000
Expected remaining maturities of debt securities held-to-maturity, amortized cost
Securities held-to-maturity, Over 5 years through 10 years, amortized cost	91,436,000
Securities held-to-maturity, Over 10 years, amortized cost	201,496,000
Total of debt securities held-to-maturity, amortized cost	292,932,000	178,413,000
Federal agency - MBS
Expected remaining maturities of debt securities available-for-sale, fair value
Securities available-for-sale, Over 1 year through 5 years, fair value	86,898,000
Securities available-for-sale, Over 5 years through 10 years, fair value	17,628,000
Fair Value	104,526,000	157,226,000
Expected remaining maturities of debt securities held-to-maturity, amortized cost
Securities held-to-maturity, Over 1 year through 5 years, amortized cost	44,145,000
Securities held-to-maturity, Over 5 years through 10 years, amortized cost	504,937,000
Securities held-to-maturity, Over 10 years, amortized cost	4,507,000
Total of debt securities held-to-maturity, amortized cost	553,589,000	445,360,000
CMOs - Federal agency
Expected remaining maturities of debt securities available-for-sale, fair value
Securities available-for-sale, One year or less, fair value	156,547,000
Securities available-for-sale, Over 1 year through 5 years, fair value	3,360,166,000
Securities available-for-sale, Over 5 years through 10 years, fair value	63,877,000
Fair Value	3,580,590,000	3,997,298,000
Expected remaining maturities of debt securities held-to-maturity, amortized cost
Securities held-to-maturity, Over 1 year through 5 years, amortized cost	816,224,000
Securities held-to-maturity, Over 5 years through 10 years, amortized cost	995,350,000
Total of debt securities held-to-maturity, amortized cost	1,811,574,000	1,781,219,000
CMOs - Non-agency
Expected remaining maturities of debt securities available-for-sale, fair value
Securities available-for-sale, One year or less, fair value	1,559,000
Securities available-for-sale, Over 1 year through 5 years, fair value	22,455,000
Fair Value	24,014,000	37,462,000
State and municipal
Expected remaining maturities of debt securities available-for-sale, fair value
Securities available-for-sale, One year or less, fair value	141,467,000
Securities available-for-sale, Over 1 year through 5 years, fair value	334,216,000
Securities available-for-sale, Over 10 years, fair value	3,348,000
Fair Value	479,031,000	415,995,000
Expected remaining maturities of debt securities held-to-maturity, amortized cost
Securities held-to-maturity, Over 1 year through 5 years, amortized cost	126,032,000
Securities held-to-maturity, Over 5 years through 10 years, amortized cost	506,974,000
Securities held-to-maturity, Over 10 years, amortized cost	49,699,000
Total of debt securities held-to-maturity, amortized cost	682,705,000	454,155,000
Other debt securities
Expected remaining maturities of debt securities available-for-sale, fair value
Securities available-for-sale, One year or less, fair value	88,286,000
Securities available-for-sale, Over 1 year through 5 years, fair value	87,883,000
Fair Value	176,169,000	178,822,000
Expected remaining maturities of debt securities held-to-maturity, amortized cost
Securities held-to-maturity, Over 1 year through 5 years, amortized cost	86,231,000
Total of debt securities held-to-maturity, amortized cost	$ 86,231,000	$ 98,696,000