Earnings Per Share (Details) - shares	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Weighted Average Number of Shares Outstanding Basic and Diluted [Line Items]
Common Stock, Shares, Outstanding	107,785,559	109,511,073
Stock Repurchased and Retired During Period, Shares	800,000	0
Treasury Stock, Shares, Acquired	600,000	700,000
Weighted Average Number of Shares Outstanding Reconciliation [Abstract]
Weighted-average number of common shares outstanding - basic	106,800,000	108,300,000
Weighted-average number of common shares outstanding - diluted	110,000,000	112,400,000
Potentially dilutive shares excluded from computation of dilutive earnings per share	2,800,000	2,300,000
Stock options
Weighted Average Number of Shares Outstanding Reconciliation [Abstract]
Incremental Common Shares Attributable to Share-based Payment Arrangements	1,200,000	1,500,000
Restricted stock units
Weighted Average Number of Shares Outstanding Reconciliation [Abstract]
Incremental Common Shares Attributable to Share-based Payment Arrangements	2,000,000	2,600,000