Earnings per Share (Details) - shares shares in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Weighted average common shares outstanding - basic	144.7	144.2
Dilutive effect of employee stock plans	2.0	1.7
Weighted average shares outstanding - diluted	146.7	145.9