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]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss), Net [Member]	Treasury Stock [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	785,165					634,559	150,606
Preferred stock cash dividends	(40,635)					(40,635)
Exercise of stock warrants into common stock					(223)			$ 223
Purchases of treasury stock	(254,000)							(254,000)
Stock-based compensation plans:
Compensation expense, net	12,801		175		6,746			5,880
Exercises of stock options, net	5,562		18		1,642			3,902
Stock purchase plan	10,594				275			10,319
Directors' stock plan	1,053		2		500			551
Deferred compensation plans, net, including dividend equivalents	28		2	(163)	232	(47)		4
Other	731				731
Common stock cash dividends	(223,074)					(223,074)
Ending balance at Jun. 30, 2016	16,471,514	1,231,500	79,979	2,201	6,690,671	8,801,305	(101,021)	(233,121)
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)