Condensed Consolidated Statements of Shareholders' Equity (Unaudited) - USD ($) $ in Thousands		Total	Preferred Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Retained Earnings [Member]	Treasury Stock [Member]
Stockholders' equity, beginning balance at Dec. 31, 2014		$ 4,697,466	$ 0	$ 134,218	$ 457,613	$ 997,452	$ 3,376,846	$ (268,663)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income (loss)		(103,479)				(497,623)	394,144
Common dividends declared ($.41 in 2015 and $.42 in 2016)		(50,694)					(50,694)
Acquisition of treasury stock		(330,066)						(330,066)
Stock-based compensation		21,877			15,026		(2,132)	8,983
Exercise of stock options		48,198			15,679		(31,789)	64,308
Stockholders' equity, ending balance at Sep. 30, 2015		4,283,302	0	134,218	488,318	499,829	3,686,375	(525,438)
Stockholders' equity, beginning balance at Jun. 30, 2015						555,319
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income (loss)		89,896
Stockholders' equity, ending balance at Sep. 30, 2015		4,283,302	0	134,218	488,318	499,829	3,686,375	(525,438)
Stockholders' equity, beginning balance at Dec. 31, 2015		4,055,552	0	130,218	482,284	231,947	3,614,369	(403,266)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income (loss)		1,325,210				910,879	414,331
Common dividends declared ($.41 in 2015 and $.42 in 2016)		(50,410)					(50,410)
Acquisition of treasury stock		(311,356)						(311,356)
Stock-based compensation		20,334			13,787		(2,224)	8,771
Exercise of stock options	[1]	47,053					(42,040)	89,093
Stockholders' equity, ending balance at Sep. 30, 2016		5,086,383	0	130,218	496,071	1,142,826	3,934,026	(616,758)
Stockholders' equity, beginning balance at Jun. 30, 2016						989,157
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income (loss)		305,538
Stockholders' equity, ending balance at Sep. 30, 2016		$ 5,086,383	$ 0	$ 130,218	$ 496,071	$ 1,142,826	$ 3,934,026	$ (616,758)

[1] Due to the prospective adoption of ASU 2016-09, the excess tax benefits from stock option exercises of $14 million at September 30, 2016 were recorded in income taxes on the Condensed Statement of Operations rather than additional paid-in-capital on the Condensed Balance Sheets. The 2015 balance of $16 million, under the previous guidance, remains in additional paid-in-capital. See further discussion at Note 2—New Accounting Standards.