Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
OPERATING ACTIVITIES
Net income	$ 147,316	$ 57,169
Adjustments to reconcile net income to cash provided by operating activities:
Provision (credit) for loan and lease losses	(10,974)	28,355
Deferred tax expense (benefit)	8,555	(11,485)
Net change in current taxes	26,703	11,829
Depreciation and amortization	27,864	26,879
Net (decrease) increase in accrued interest payable	(4,264)	(4,624)
Net increase in income earned not collected	(2,328)	(1,914)
Contribution to pension plans	0	(100,000)
Realized gains on investment securities available for sale, net	(9,207)	(19,795)
Marketable equity securities (gains) losses, net	(16,011)	51,408
Origination of loans held for sale	(315,451)	(205,986)
Proceeds from Sale of Loans Held-for-sale	279,180	201,886
Gain on sale of loans	(9,365)	(5,682)
Net (gains) losses on other real estate owned	(527)	1,419
Net accretion of premiums and discounts	116	4,674
Amortization of intangible assets	5,795	6,160
Origination of mortgage servicing rights, net of change in valuation allowance	(6,567)	1,384
Net change in other assets	17,535	4,067
Net change in other liabilities	(33,494)	(28,135)
Net cash provided by operating activities	104,876	17,609
INVESTING ACTIVITIES
Net increase in loans outstanding	(383,507)	(202,667)
Purchases of investment securities available for sale	(1,737,890)	(4,305,818)
Purchases of investment securities held to maturity	(207,313)	(724,412)
Purchases of marketable equity securities	(306)	(287,014)
Proceeds from maturities/calls of investment securities held to maturity	206,282	14,166
Proceeds from maturities/calls of investment securities available for sale	1,079,216	572,937
Proceeds from sales of investment securities available for sale	351,984	3,156,988
Proceeds from sales of marketable equity securities	1,111	2,438
Net (increase) decrease in overnight investments	(3,241,421)	454,455
Cash paid to FDIC for settlement of shared-loss agreement	(16,103)	(99,468)
Proceeds from sales of other real estate	10,011	5,265
Proceeds from sales of premises and equipment	1,143	0
Purchases of premises and equipment	(23,544)	(26,930)
Business acquisitions, net of cash acquired	0	(1,235)
Other investing activities	(8,009)	0
Net cash used in investing activities	(3,968,346)	(1,441,295)
FINANCING ACTIVITIES
Net decrease in time deposits	(159,035)	(310,224)
Net increase in demand and other interest-bearing deposits	4,058,956	1,017,371
Net decrease in short-term borrowings	39,218	(92,871)
Repayments of Other Long-term Debt	(17,973)	(38,583)
Origination of long-term obligations	0	745,886
Net proceeds from preferred stock issuance	0	339,958
Repurchase of common stock	0	(156,094)
Cash dividends paid	(9,249)	(4,256)
Net cash (used in) provided by financing activities	3,911,917	1,501,187
Change in cash and due from banks	48,447	77,501
Cash and due from banks at beginning of period	362,048	376,719
Cash and due from banks at end of period	410,495	454,220
SUPPLEMENTAL DISCLOSURE OF NONCASH INVESTING AND FINANCING ACTIVITIES:
Interest	19,935	35,783
Income taxes	11	(592)
Transfers of loans to other real estate	2,374	4,560
Dividends declared but not paid	4,614	4,141
Unsettled call of investment securities	3,000	0
Loans held for sale exchanged for investment securities	63,526	0
Reclassification of portfolio loans to loans held for sale	22,655	1,304
Transfers of premises and equipment to other real estate	4,732	1,427
Premises and equipment acquired through finance leases and other financing arrangements	0	1,191
Unsettled common stock repurchases	$ 0	$ 3,610