Shareholders' Equity - Schedule of Stock Repurchases (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	1 Months Ended	3 Months Ended		6 Months Ended		72 Months Ended
	Jul. 31, 2017	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Mar. 31, 2018
Class of Stock [Line Items]
Shares purchased (in shares)						115.0
Total repurchase cost				$ 955	$ 1,160	$ 10,500
2012 - Share Repurchase Program
Class of Stock [Line Items]
Shares purchased (in shares)	0.5	2.8	8.0	6.7	9.1
Average price per share of stock repurchased (in dollars per share)	$ 133.24	$ 141.23	$ 128.54	$ 141.06	$ 126.85
Total repurchase cost	$ 60	$ 400	$ 1,030	$ 950	$ 1,154
Additional associated costs		2	5	5	6
Total repurchase and associated costs		$ 402	$ 1,035	$ 955	$ 1,160