Earnings Per Share (Details) - shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Weighted Average Number of Shares Outstanding Basic and Diluted [Line Items]
Common stock, shares, outstanding	106,684,084	107,906,644	105,640,003
Repurchased and retired common stock	3,267,881	0	7,690,628
Treasury Stock, Shares, Acquired	700,000	700,000	700,000
Weighted Average Number of Shares Outstanding Reconciliation [Abstract]
Weighted-average number of common shares outstanding - basic	108,100,000	107,000,000	108,800,000
Adjusted weighted average shares and assumed conversions - diluted	110,900,000	109,200,000	110,600,000
Potentially dilutive shares excluded from computation of dilutive earnings per share	3,100,000	3,600,000	5,500,000
Stock options
Weighted Average Number of Shares Outstanding Reconciliation [Abstract]
Incremental common shares attributable to share-based payment arrangements	1,300,000	800,000	200,000
Stock-settled stock appreciation rights
Weighted Average Number of Shares Outstanding Reconciliation [Abstract]
Incremental common shares attributable to share-based payment arrangements	0	0	300,000
Restricted stock units
Weighted Average Number of Shares Outstanding Reconciliation [Abstract]
Incremental common shares attributable to share-based payment arrangements	1,500,000	1,400,000	1,300,000