Earnings Per Share (Reconciliation of Basic Shares Outstanding to Diluted Shares Outstanding) (Details) - shares shares in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Earnings Per Share [Abstract]
Basic shares outstanding	51.9	53.3	52.5	53.7
Dilutive effect of common stock equivalents	0.7	0.4	0.7	0.4
Diluted shares outstanding	52.6	53.7	53.2	54.1