Reconciliation of Weighted Average Number of Shares of Common Stock Outstanding (Details) - shares shares in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Earnings Per Share [Abstract]
Weighted average common shares outstanding - basic	258.0	262.2	258.0	262.6
Dilutive effect of stock options	4.7	5.0	4.7	5.0
Weighted average common shares outstanding - diluted	262.7	267.2	262.7	267.6
Antidilutive stock options outstanding	1.3	1.0	2.0	2.2