Consolidated Statement of Changes in Shareholders' Equity - USD ($) $ in Thousands	Total	Series D Preferred Stock [Member]	Series F Preferred Stock [Member]	Series A Warrants [Member]	Preferred Stock [Member]	Preferred Stock [Member] Series D Preferred Stock [Member]	Preferred Stock [Member] Series F Preferred Stock [Member]	Common Stock [Member]	Common Stock Issuable [Member]	Additional Paid-in Capital [Member]	Additional Paid-in Capital [Member] Series F Preferred Stock [Member]	Additional Paid-in Capital [Member] Series A Warrants [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss), Net [Member]	Treasury Stock [Member]	Treasury Stock [Member] Series A Warrants [Member]
Beginning balance at Dec. 31, 2015	$ 16,173,289				$ 1,231,500			$ 79,782	$ 2,364	$ 6,680,768			$ 8,430,502	$ (251,627)
Total comprehensive income	1,272,105												1,315,114	(43,009)
Preferred stock cash dividends	(81,270)												(81,270)
Redemption of Series D Preferred Stock		$ (500,000)				$ (500,000)
Issuance of preferred stock			$ 495,000				$ 500,000				$ (5,000)
Exercise of stock warrants into common stock				$ (2)								$ (4,750)				$ 4,748
Purchases of treasury stock	(641,334)														$ (641,334)
Stock-based compensation plans:
Compensation expense, net	27,290							169		16,132					10,989
Exercises of stock options, net	169,617							18		(12,190)					181,789
Stock purchase plan	10,594									275					10,319
Directors’ stock plan	2,080							2		535					1,543
Deferred compensation plans, net, including dividend equivalents	3							2	(219)	163			(93)		150
Other	1,015									1,015
Common stock cash dividends	(441,765)												(441,765)
Ending balance at Dec. 31, 2016	16,486,622				1,231,500			79,973	2,145	6,676,948			9,222,488	(294,636)	(431,796)
Total comprehensive income	1,403,157												1,408,306	(5,149)
Reclassification of income tax effects to retained earnings	64,029												64,029	(64,029)
Preferred stock cash dividends	(72,734)												(72,734)
Exercise of stock warrants into common stock												(28,746)				28,746
Purchases of treasury stock	(1,205,905)														(1,205,905)
Stock-based compensation plans:
Compensation expense, net	12,004							(64)		(47,670)					59,738
Exercises of stock options, net	72,274									(12,142)					84,416
Stock purchase plan	10,831									2,563					8,268
Directors’ stock plan	1,926									270					1,656
Deferred compensation plans, net, including dividend equivalents	(156)								(298)	(368)			(85)		595
Common stock cash dividends	(457,200)												(457,200)
Ending balance at Dec. 31, 2017	16,250,819				1,231,500			79,909	1,847	6,590,855			10,164,804	(363,814)	(1,454,282)
Cumulative effect of change in accounting principle — equity securities	(16,853)												16,853	(16,853)
Total comprehensive income	1,878,666												1,918,080	(39,414)
Preferred stock cash dividends	(72,521)												(72,521)
Exercise of stock warrants into common stock												$ (22,394)				$ 22,394
Purchases of treasury stock	(2,194,396)														(2,194,396)
Stock-based compensation plans:
Compensation expense, net	34,908							(26)		12,421					22,513
Exercises of stock options, net	59,766									(3,793)					63,559
Stock purchase plan	11,124									2,358					8,766
Directors’ stock plan	2,337									162					2,175
Deferred compensation plans, net, including dividend equivalents	(54)								(121)	(267)			(86)		420
Common stock cash dividends	(510,458)												(510,458)
Ending balance at Dec. 31, 2018	$ 15,460,191				$ 1,231,500			$ 79,883	$ 1,726	$ 6,579,342			$ 11,516,672	$ (420,081)	$ (3,528,851)