Fair Value Measurements, Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands		Mar. 31, 2016	Dec. 31, 2015
Financial assets
Cash and due from banks		$ 287,183	$ 374,921
Interest-bearing deposits in other financial institutions		68,025	79,764
Federal funds sold and securities purchased under agreements to resell		20,200	19,000
Investment securities held to maturity		1,176,821	1,168,230
Investment securities held to maturity, fair value		1,204,345	1,184,442
Investment securities available for sale		4,905,841	4,967,414
FHLB and Federal Reserve Bank stocks		181,853	147,240
Loans held for sale		128,339	124,915
Loans, net		18,949,870	18,440,079
Derivatives (trading and other assets)		53,087	32,192
Financial liabilities
Short-term funding		1,417,408	834,416
Long-term funding	[1]	2,861,316	2,676,164
Derivatives (trading and other liabilities)		55,223	33,430
Fair Value, Inputs, Level 1 [Member]
Financial assets
Cash and due from banks		287,183	374,921
Cash and due from banks, Fair Value		287,183	374,921
Interest-bearing deposits in other financial institutions		68,025	79,764
Interest-bearing deposits in other financial institutions, fair value		68,025	79,764
Federal funds sold and securities purchased under agreements to resell		20,200	19,000
Federal funds sold and securities purchased under agreements to resell, fair value		20,200	19,000
Investment securities available for sale		2,605	2,566
Investment securities available for sale, at fair value		2,605	2,566
Fair Value, Inputs, Level 2 [Member]
Financial assets
Investment securities held to maturity		1,176,821	1,168,230
Investment securities held to maturity, fair value		1,204,345	1,184,442
Investment securities available for sale		4,903,036	4,964,648
Investment securities available for sale, at fair value		4,903,036	4,964,648
FHLB and Federal Reserve Bank stocks		181,853	147,240
Federal Home Loan Bank and Federal Reserve Bank stocks, fair value		181,853	147,240
Loans held for sale		128,339	124,915
Loans held for sale, fair value		129,398	124,915
Bank owned life insurance		580,583	583,019
Bank owned life insurance, fair value		580,583	583,019
Derivatives (trading and other assets)		55,315	34,907
Derivatives (trading and other assets), fair value		55,315	34,907
Financial liabilities
Brokered CDs and other time deposits		1,568,042	1,562,802
Brokered CDs and other time deposits, fair value		1,576,714	1,564,464
Short-term funding		1,417,408	834,416
Short-term funding, fair value		1,417,408	834,416
Long-term funding		2,861,316	2,676,164
Long-term funding, fair value		2,925,447	2,728,112
Standby letters of credit		2,746	2,954
Standby letters of credit, fair value		2,746	2,954
Derivatives (trading and other liabilities)		57,451	36,145
Derivatives (trading and other liabilities), fair value		57,451	36,145
Fair Value, Inputs, Level 3 [Member]
Financial assets
Investment securities available for sale		200	200
Investment securities available for sale, at fair value		200	200
Loans, net		18,949,870	18,440,079
Loans, net, fair value		19,025,680	18,389,832
Derivatives (trading and other assets)		2,689	1,361
Derivatives (trading and other assets), fair value		2,689	1,361
Financial liabilities
Noninterest-bearing demand, savings, interest-bearing demand, and money market accounts		19,117,418	19,444,863
Noninterest-bearing demand, savings, interest-bearing demand, and money market deposits, fair value		19,117,418	19,444,863
Derivatives (trading and other liabilities)		1,732	0
Derivatives (trading and other liabilities), fair value		$ 1,732	$ 0

[1] During the first quarter of 2016, the Corporation adopted a new accounting standard related to simplifying the presentation of debt issuance costs. Under this new accounting standard, debt issuance costs are still capitalized; however, they are reflected on the balance sheet with the related debt issued rather than within other assets. All prior periods have been restated to reflect this change in presentation. See Note 3 for additional information on this new accounting standard.