Consolidated Statement of Changes in Shareholders' Equity - USD ($) $ in Thousands	Total	Preferred Stock [Member]	Common Stock [Member]	Additional Paid-In Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss), Net of Tax [Member]	Treasury Stock [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of accounting change	$ (2,285)				$ (2,285)
Adjusted beginning balance	3,295,578	$ 144,486	$ 642	$ 953,361	2,184,784	$ 79,512	$ (67,207)
Balance at Dec. 31, 2017	3,297,863	144,486	642	953,361	2,187,069	79,512	(67,207)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	454,918				454,918
Other comprehensive income, net of tax	(152,647)					(152,647)
Reclassification of certain income tax effects related to the change in the U.S. statutory federal income tax rate under the Tax Cuts and Jobs Act					(9,535)	9,535
Proceeds from stock option exercises/stock unit conversions (408,563 shares, 399,224 shares, and 548,238 shares during 2020, 2019, and 2018, respectively)	31,647				(16,653)		48,300
Stock-based compensation expense recognized in earnings	13,943			13,943
Purchase of treasury stock (206,951 shares, 716,062 shares, and 1,037,982 shares during 2020, 2019, and 2018, respectively)	(101,010)						(101,010)
Treasury stock issued to the 401(k) stock purchase plan (140,264 shares)	0
Cash dividends paid on preferred stock (approximately $0.34 per share in 2020 and $1.34 per share in 2019 and 2018)	(8,063)				(8,063)
Cash dividends – common stock ($2.85 per share, $2.80 per share, and $2.58 per share in 2020, 2019, and 2018, respectively)	(165,449)				(165,449)
Balance at Dec. 31, 2018	3,368,917	144,486	642	967,304	2,440,002	(63,600)	(119,917)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of accounting change	(14,672)				(14,672)
Adjusted beginning balance	3,354,245	144,486	642	967,304	2,425,330	(63,600)	(119,917)
Net income	443,599				443,599
Other comprehensive income, net of tax	330,970					330,970
Proceeds from stock option exercises/stock unit conversions (408,563 shares, 399,224 shares, and 548,238 shares during 2020, 2019, and 2018, respectively)	20,770				(16,326)		37,096
Stock-based compensation expense recognized in earnings	15,946			15,946
Purchase of treasury stock (206,951 shares, 716,062 shares, and 1,037,982 shares during 2020, 2019, and 2018, respectively)	(68,793)						(68,793)
Treasury stock issued to the 401(k) stock purchase plan (140,264 shares)	0
Cash dividends paid on preferred stock (approximately $0.34 per share in 2020 and $1.34 per share in 2019 and 2018)	(8,063)				(8,063)
Cash dividends – common stock ($2.85 per share, $2.80 per share, and $2.58 per share in 2020, 2019, and 2018, respectively)	(177,006)				(177,006)
Balance at Dec. 31, 2019	3,911,668	144,486	642	983,250	2,667,534	267,370	(151,614)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of accounting change	(29,252)				(29,252)
Adjusted beginning balance	3,882,416	144,486	642	983,250	2,638,282	267,370	(151,614)
Net income	331,151				331,151
Other comprehensive income, net of tax	245,600					245,600
Proceeds from stock option exercises/stock unit conversions (408,563 shares, 399,224 shares, and 548,238 shares during 2020, 2019, and 2018, respectively)	12,557				(27,214)		39,771
Stock-based compensation expense recognized in earnings	13,918			13,918
Redemption of series A preferred stock (6,000,000 shares)	(150,000)	(144,486)			(5,514)
Issuance of series B preferred stock (150,000 shares)	145,452	145,452
Purchase of treasury stock (206,951 shares, 716,062 shares, and 1,037,982 shares during 2020, 2019, and 2018, respectively)	(15,785)						(15,785)
Treasury stock issued to the 401(k) stock purchase plan (140,264 shares)	10,307				(3,382)		13,689
Cash dividends paid on preferred stock (approximately $0.34 per share in 2020 and $1.34 per share in 2019 and 2018)	(2,016)				(2,016)
Cash dividends – common stock ($2.85 per share, $2.80 per share, and $2.58 per share in 2020, 2019, and 2018, respectively)	(180,584)				(180,584)
Balance at Dec. 31, 2020	$ 4,293,016	$ 145,452	$ 642	$ 997,168	$ 2,750,723	$ 512,970	$ (113,939)