Consolidated Statements of Cash Flows - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash Flows from Operating Activities
Net income		$ 306,771	$ 326,790	$ 333,562
Adjustments to reconcile net income to net cash provided by operating activities:
Provision for credit losses		174,006	16,000	0
Depreciation and amortization		50,567	58,149	48,253
Addition to (recovery of) valuation allowance on mortgage servicing rights, net		17,704	63	(545)
Amortization of mortgage servicing rights		22,664	12,432	9,594
Amortization of other intangible assets		10,192	9,948	8,159
Amortization and accretion on earning assets, funding, and other, net		25,028	23,573	11,624
Net amortization of tax credit investments		25,556	20,062	19,425
Losses (gains) on sales of investment securities, net		(9,222)	(5,957)	1,985
Asset (gains) losses, net	[1]	(155,589)	(2,713)	1,103
(Gains) on sale of branches, net		(7,449)	0	0
(Gain) loss on mortgage banking activities, net		(59,379)	(20,120)	(22,497)
Mortgage loans originated for sale		(1,642,135)	(1,090,792)	(1,092,318)
Proceeds from sales of mortgage loans held for sale		1,959,571	1,317,077	1,131,652
Pension contributions		0	0	(41,877)
(Increase) decrease in interest receivable		933	7,595	(7,417)
Increase (decrease) in interest payable		(11,385)	2,495	10,407
Increase (decrease) in accrued expenses		(29,057)	723	30,924
Increase (decrease) in derivative position		(113,760)	(102,966)	40,950
Increase (decrease) in net income tax position		(47,268)	43,908	18,178
Net change in other assets and other liabilities		32,270	(42,005)	(4,594)
Net cash provided by operating activities		550,020	574,260	496,567
Cash Flows from Investing Activities
Net increase in loans		(1,640,524)	(137,990)	(326,464)
Purchases of
AFS securities		(1,648,938)	(460,124)	(737,580)
HTM securities		(125,480)	(423,682)	(682,622)
Federal Home Loan Bank and Federal Reserve Bank stocks		(84,152)	(246,836)	(347,323)
Premises, equipment, and software		(54,682)	(67,459)	(65,854)
Other intangibles		(200)	0	0
Proceeds from
Sales of AFS securities		626,283	1,367,476	601,130
Sale of Federal Home Loan Bank and Federal Reserve Bank stocks		144,000	270,023	282,145
Prepayments, calls, and maturities of AFS investment securities		1,343,056	561,659	633,859
Prepayments, calls, and maturities of HTM investment securities		449,078	260,510	217,836
Sales, prepayments, calls and maturities of other assets		27,964	10,250	41,856
Net change in tax credit and alternative investments		(55,134)	(67,632)	(57,327)
Net cash (paid) received in acquisitions		31,518	551,250	59,472
Net cash provided by (used in) investing activities		(793,737)	1,617,446	(380,872)
Cash Flows from Financing Activities
Net increase (decrease) in deposits		2,497,378	(1,842,748)	270,481
Net decrease in deposits due to branch sales		(222,878)	0	0
Net increase (decrease) in short-term funding		(238,655)	308,039	(581,371)
Net increase (decrease) in short-term FHLB advances		(520,000)	(380,000)	616,000
Repayment of long-term FHLB advances		(1,040,972)	(764,657)	(2,150,016)
Proceeds from long-term FHLB advances		4,215	751,573	1,837,680
Redemption of Corporation's senior notes		0	(250,000)	0
Repayment of finance lease principal		(1,081)	(1)	0
Proceeds from issuance of long-term funding		0	0	300,000
Proceeds from issuance of preferred shares		96,796	0	97,315
Proceeds from issuance of common stock for stock-based compensation plans		3,966	11,216	18,408
Common stock warrants exercised		0	0	(1)
Purchase of preferred shares		0	0	(537)
Purchase of common stock returned to authorized but unissued		0	0	(33,075)
Cash dividends on common stock		(112,023)	(111,804)	(105,519)
Cash dividends on preferred stock		(18,358)	(15,202)	(10,784)
Net cash provided by (used in) financing activities		371,020	(2,479,660)	44,983
Net increase (decrease) in cash, cash equivalents, and restricted cash		127,304	(287,954)	160,678
Cash, cash equivalents, and restricted cash at beginning of period		588,744	876,698	716,018
Cash, cash equivalents, and restricted cash at end of period		716,048	588,744	876,698
Supplemental disclosures of cash flow information
Cash paid for interest		159,291	332,919	261,724
Cash paid for income and franchise taxes		17,734	41,131	18,335
Loans and bank premises transferred to OREO		19,261	10,513	26,517
Capitalized mortgage servicing rights		13,667	11,606	10,722
Loans transferred into held for sale from portfolio, net		264,570	313,570	33,010
Transfer of HTM securities to AFS securities (adoption of ASU 2019-04)		0	692,414	0
Unsettled trades to purchase securities		0	0	883
Acquisitions
Total cash, cash equivalents, and restricted cash shown on the consolidated statements of cash flows		588,744	588,744	716,018
ABRC [Member]
Proceeds from
Net cash received in ABRC sale		256,511	0	0
Performance/Service Based RSAs, RSA, [Member]
Cash Flows from Financing Activities
Payments for Repurchase of Common Stock		6,113	8,592	7,148
Board Authorized Purchase Program [Member]
Cash Flows from Financing Activities
Payments for Repurchase of Common Stock		$ 71,255	$ 177,484	$ 206,450

[1] (b) The year ended December 31, 2020 includes a gain of $163 million from the sale of ABRC. The year ended December 31, 2019 includes less than $1 million of Huntington related asset losses. The year ended December 31, 2018 includes approximately $2 million of Bank Mutual acquisition related asset losses net of asset gains.