Reconciliation of Weighted Average Number of Shares of Common Stock Outstanding (Details) - shares shares in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Earnings Per Share [Abstract]
Weighted average common shares outstanding - basic	131.1	133.7	131.3	135.5
Dilutive effect of stock options	2.5	2.3	2.5	2.4
Weighted average common shares outstanding - diluted	133.6	136.0	133.8	137.9
Antidilutive stock options outstanding	0.5	1.2	1.1	1.2