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	491,793							528,301	(36,508)
Preferred stock cash dividends	(40,635)							(40,635)
Exercise of stock warrants into common stock				$ 1			$ (1)
Stock-based compensation plans:
Compensation expense, net	21,110		144			20,966
Exercises of stock options, net	35,116		179			34,937
Stock purchase plan	10,346		45			10,301
Directors' stock plan	830		3			827
Deferred compensation plans, net, including dividend equivalents	(51)		2		(276)	274		(51)
Other	801					801
Common stock cash dividends - $1.40 per share	(187,209)							(187,209)
Ending balance at Jun. 30, 2015	12,667,997	1,231,500	66,531		2,332	3,477,611		8,107,525	(217,502)
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 - $1.40 per share	(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)