Consolidated Statements of Changes in Shareholders Equity - USD ($)	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Retained Earnings [Member]	Stockholders' Equity, Total [Member]
Balance, shares at Dec. 31, 2012		143,697,178
Balance at Dec. 31, 2012		$ 1,400,000	$ 1,012,300,000	$ (145,200,000)	$ 1,127,900,000	$ 1,996,400,000
Net income (loss)	$ (621,400,000)				(621,400,000)	(621,400,000)
Equity in joint venture	(2,200,000)				(508,700,000)
Employee equity awards, shares		1,979,066
Employee equity awards, value			0			12,600,000
Stock forfeitures, shares		668,263
Net shares settled		240,359
Payments Related to Tax Withholding for Share-based Compensation	0
Stock Forfeitures, value			(12,600,000)			0
Excess tax benefits from share-based payment arrangements			100,000			100,000
SERP shares issued		30,501
Other Comprehensive Income	$ 90,600,000			90,600,000		90,600,000
Balance, shares at Dec. 31, 2013	144,800,000	144,798,123
Balance at Dec. 31, 2013		$ 1,400,000	1,025,000,000	(54,600,000)		1,480,500,000
Net income (loss)	$ 358,800,000					358,800,000
Employee equity awards, shares		719,214
Employee equity awards, value			8,200,000			8,200,000
Stock forfeitures, shares		249,444
Net shares settled		256,332
Payments Related to Tax Withholding for Share-based Compensation	$ 0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross	0
Excess tax benefits from share-based payment arrangements			2,400,000			2,400,000
SERP shares issued		77,562
Stock Repurchased During Period, Value	$ 129,200,000
Other Comprehensive Income	$ (99,200,000)			(99,200,000)		(99,200,000)
Balance, shares at Dec. 31, 2014	141,100,000	141,089,123
Balance at Dec. 31, 2014	$ 1,621,500,000	$ 1,400,000	1,035,600,000	(153,800,000)	867,500,000	1,621,500,000
Treasury Stock, Carrying Basis	(4,000,000)
Treasury Stock, Value	(129,200,000)
Net income (loss)	788,700,000					788,700,000
Employee equity awards, shares		653,011
Employee equity awards, value			26,000,000			26,000,000
Stock forfeitures, shares		170,789
Net shares settled		395,447
Payments Related to Tax Withholding for Share-based Compensation	$ (20,700,000)
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross	0
Excess tax benefits from share-based payment arrangements			10,700,000			10,700,000
SERP shares issued		133,677
Stock Repurchased During Period, Value	$ (300,000,000)
Other Comprehensive Income	$ (6,700,000)			(6,700,000)		(6,700,000)
Balance, shares at Dec. 31, 2015	135,600,000	135,617,710
Balance at Dec. 31, 2015	$ 2,119,500,000	$ 1,400,000	$ 1,051,600,000	$ (160,500,000)	$ 1,656,200,000	$ 2,119,500,000
Treasury Stock, Carrying Basis	(5,691,865)
Treasury Stock, Value	$ (429,200,000)