Reconciliation of Weighted Average Number of Shares of Common Stock Outstanding (Details) - shares shares in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Earnings Per Share [Abstract]
Weighted average common shares outstanding - basic	130.9	134.8	131.4	136.4
Dilutive effect of stock options	2.5	2.5	2.6	2.5
Weighted average common shares outstanding - diluted	133.4	137.3	134.0	138.9
Antidilutive stock options outstanding	1.1	1.1	1.1	1.8