Earnings Per Share (Reconciliation of Basic Shares Outstanding to Diluted Shares Outstanding) (Details) - shares shares in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Earnings Per Share [Abstract]
Basic shares outstanding	53.3	55.4	55.5
Dilutive effect of common stock equivalents	0.6	0.3	0.4
Diluted shares outstanding	53.9	55.7	55.9