Consolidated Statement of Changes in Shareholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Preferred Stock [Member]	Common Stock [Member]	Common Stock [Member] Series A Warrants [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, 2014	$ 12,335,896	$ 1,231,500	$ 66,157		$ 2,608	$ 3,409,506		$ 7,807,119	$ (180,994)
Total comprehensive income	826,223							808,702	17,521
Preferred stock cash dividends	(60,953)							(60,953)
Exercise of stock warrants into common stock				$ 1			$ (1)
Stock-based compensation plans:
Compensation expense, net	31,559		143			31,416
Exercises of stock options, net	57,418		285			57,133
Stock purchase plan	10,346		45			10,301
Directors' stock plan	1,350		4			1,346
Deferred compensation plans, net, including dividend equivalents	(51)		2		(267)	290		(76)
Other	1,191					1,191
Common stock cash dividends - $2.10 per share	(281,045)							(281,045)
Ending balance at Sep. 30, 2015	12,921,934	1,231,500	66,637		2,341	3,511,182		8,273,747	(163,473)
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	1,121,611							984,543	137,068
Preferred stock cash dividends	(60,953)							(60,953)
Exercise of stock warrants into common stock							$ (223)				$ 223
Purchases of treasury stock	(604,000)									$ (604,000)
Stock-based compensation plans:
Compensation expense, net	18,376		171			7,315				10,890
Exercises of stock options, net	11,411		18			(183)				11,576
Stock purchase plan	10,594					275				10,319
Directors' stock plan	1,575		2			526				1,047
Deferred compensation plans, net, including dividend equivalents	28		2		(140)	232		(70)		4
Other	1,102					1,102
Common stock cash dividends - $2.10 per share	(332,057)							(332,057)
Ending balance at Sep. 30, 2016	$ 16,340,976	$ 1,231,500	$ 79,975		$ 2,224	$ 6,689,812		$ 9,021,965	$ (114,559)	$ (569,941)