Equity - Accelerated Share Repurchase Program (Details) - USD ($) $ / shares in Units, shares in Millions					1 Months Ended	3 Months Ended	12 Months Ended
	Oct. 31, 2017	Aug. 01, 2017	Dec. 07, 2016	Sep. 07, 2016	Dec. 31, 2015	Dec. 07, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accelerated Share Repurchases [Line Items]
Total number of shares purchased (in shares)					0.3
Average price paid per share (in dollars per share)					$ 98.98		$ 147.74	$ 113.36	$ 99.00
Accelerated Share Repurchases, August 2017
Accelerated Share Repurchases [Line Items]
Authorized amount		$ 500,000,000
Accelerated share repurchase, settlement (payment) or receipt		$ (500,000,000)
Total number of shares purchased (in shares)	3.2
Average price paid per share (in dollars per share)	$ 154.46
Accelerated Share Repurchases, August 2017 | Initial Award
Accelerated Share Repurchases [Line Items]
Total number of shares purchased (in shares)		2.8
Authorized amount repurchased (as a percent)		85.00%
Accelerated Share Repurchases, August 2017 | Additional Award
Accelerated Share Repurchases [Line Items]
Total number of shares purchased (in shares)	0.5
Accelerated Share Repurchases, September 2016
Accelerated Share Repurchases [Line Items]
Authorized amount				$ 750,000,000
Accelerated share repurchase, settlement (payment) or receipt				$ (750,000,000)
Total number of shares purchased (in shares)			0.9			6.1
Average price paid per share (in dollars per share)						$ 122.18
Accelerated Share Repurchases, September 2016 | Initial Award
Accelerated Share Repurchases [Line Items]
Total number of shares purchased (in shares)				4.4
Accelerated Share Repurchases, September 2016 | Additional Award
Accelerated Share Repurchases [Line Items]
Total number of shares purchased (in shares)				0.9