Consolidated Statement of Changes in Shareholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Preferred Stock [Member]	Common Stock [Member]	Common Stock Issuable [Member]	Additional Paid-in Capital [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, 2016	$ 16,486,622	$ 1,231,500	$ 79,973	$ 2,145	$ 6,676,948		$ 9,222,488	$ (294,636)	$ (431,796)
Total comprehensive income	754,535						729,980	24,555
Preferred stock cash dividends	(36,474)						(36,474)
Exercise of stock warrants into common stock						$ (10,443)				$ 10,443
Purchases of treasury stock	(756,967)								(756,967)
Stock-based compensation plans:
Compensation expense, net	(2,521)		(62)		(58,749)				56,290
Exercises of stock options, net	57,074				(5,354)				62,428
Stock purchase plan	10,831				2,563				8,268
Directors’ stock plan	965				173				792
Deferred compensation plans, net, including dividend equivalents	(55)			(205)	(208)		(43)		401
Common stock cash dividends	(230,473)						(230,473)
Ending balance at Jun. 30, 2017	16,283,537	1,231,500	79,911	1,940	6,604,930		9,685,478	(270,081)	(1,050,141)
Beginning 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 principles- equity securities	(16,853)						16,853	(16,853)
Total comprehensive income	708,496						845,770	(137,274)
Preferred stock cash dividends	(36,260)						(36,260)
Exercise of stock warrants into common stock						$ (5,123)				$ 5,123
Purchases of treasury stock	(1,196,062)								(1,196,062)
Stock-based compensation plans:
Compensation expense, net	15,446		(25)		(6,194)				21,665
Exercises of stock options, net	50,671				(2,402)				53,073
Stock purchase plan	11,124				2,358				8,766
Directors’ stock plan	1,192				149				1,043
Deferred compensation plans, net, including dividend equivalents	(49)			(156)	(248)		(37)		392
Common stock cash dividends	(227,492)						(227,492)
Ending balance at Jun. 30, 2018	$ 15,577,885	$ 1,231,500	$ 79,884	$ 1,691	$ 6,579,395		$ 10,763,638	$ (517,941)	$ (2,560,282)