Shareholders' Equity - Schedule of Stock Repurchases (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	1 Months Ended	3 Months Ended		9 Months Ended		78 Months Ended
	Oct. 26, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018
Class of Stock [Line Items]
Shares purchased (in shares)						117.0
Total repurchase cost				$ 1,256.0	$ 1,913.0	$ 10,800.0
2012 - Share Repurchase Program
Class of Stock [Line Items]
Shares purchased (in shares)		2.1	5.4	8.8	14.5
Average price per share of stock repurchased (in dollars per share)		$ 145.71	$ 139.61	$ 142.15	$ 131.58
Total repurchase cost		$ 300.0	$ 749.0	$ 1,250.0	$ 1,903.0
Additional associated costs		1.0	4.0	6.0	10.0
Total repurchase and associated costs		$ 301.0	$ 753.0	$ 1,256.0	$ 1,913.0
Subsequent Event | 2012 - Share Repurchase Program
Class of Stock [Line Items]
Shares purchased (in shares)	0.2
Average price per share of stock repurchased (in dollars per share)	$ 146.52
Total repurchase cost	$ 24.2