Earnings Per Share - Number of Shares Used in Earnings Per Share Calculations (Details) - shares shares in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Earnings Per Share [Abstract]
Weighted average basic shares outstanding (shares)	145.5	147.3	146.2	150.7
Dilutive effect of weighted average number of stock options (shares)	0.3	1.0	0.4	0.9
Weighted average diluted shares outstanding (shares)	145.8	148.3	146.6	151.6