New Accounting Standards (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Tax expense	[1]	$ (327)	$ (291)	$ (940)	$ (802)
Accounting Standards Update 2016-09 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Tax expense		$ 11		$ 47

[1] Includes the prospective adoption of ASU 2016-09 in 2017. See New Accounting Standards in Note 2 for additional information.