Parent Company Only Financial Information, Statement of Cash Flows (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Cash Flows from Operating Activities
Net income	$ 350,994	$ 306,771	$ 326,790
Adjustments to reconcile net income to net cash provided by operating activities:
Losses (gains) on sales of investment securities, net	16	(9,222)	(5,957)
Net change in other assets and other liabilities	54,520	32,270	(42,005)
Net cash provided by operating activities	529,551	550,020	574,260
Cash Flows from Investing Activities
Proceeds from sales of investment securities	158,743	626,283	1,367,476
Net cash provided by (used in) investing activities	(1,584,186)	(793,737)	1,617,446
Cash Flows from Financing Activities
Net increase (decrease) in commercial paper	101,946	(238,655)	308,039
Redemption of Corporation's senior notes	300,000	0	250,000
Proceeds from issuance of common stock for stock-based compensation plans	25,702	3,966	11,216
Proceeds from issuance of preferred stock	0	96,796	0
Redemption of preferred stock	(164,458)	0	0
Cash dividends on common stock	(116,061)	(112,023)	(111,804)
Cash dividends on preferred stock	(17,111)	(18,358)	(15,202)
Net cash used in financing activities	1,364,102	371,020	(2,479,660)
Performance/Service Based RSAs, RSA, [Member]
Cash Flows from Financing Activities
Payments for Repurchase of Common Stock	(4,847)	(6,113)	(8,592)
Parent Company Only
Cash Flows from Operating Activities
Net income	350,994	306,771	326,790
Adjustments to reconcile net income to net cash provided by operating activities:
(Increase) decrease in equity in undistributed net income (loss) of subsidiaries	28,802	(61,406)	(21,789)
Net change in other assets and other liabilities	17,102	(49,890)	265
Net cash provided by operating activities	396,898	195,475	305,266
Cash Flows from Investing Activities
Net (increase) decrease in notes receivable from subsidiaries	20,000	(105,000)	250,000
Net cash provided by (used in) investing activities	20,000	(105,000)	250,000
Cash Flows from Financing Activities
Net increase (decrease) in commercial paper	(24,616)	27,330	(13,406)
Redemption of Corporation's senior notes	0	0	(250,000)
Proceeds from issuance of common stock for stock-based compensation plans	25,702	3,966	11,216
Proceeds from issuance of preferred stock	0	96,796	0
Purchase of treasury stock, open market purchases	(132,955)	(71,255)	(177,484)
Cash dividends on common stock	(116,061)	(112,023)	(111,804)
Cash dividends on preferred stock	(17,111)	(18,358)	(15,202)
Net cash used in financing activities	(434,346)	(79,656)	(565,272)
Net increase (decrease) in cash and cash equivalents	(17,448)	10,819	(10,006)
Cash and cash equivalents at beginning of year	55,432	44,613	54,619
Cash and cash equivalents at end of year	37,984	55,432	44,613
Redemption of preferred stock	$ (164,458)	$ 0	$ 0