Stock-Based Compensation (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions		3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Compensation
Stock-based compensation expense		$ 53	$ 50	$ 108	$ 107
Options, grants in period (in shares)		4
Options, grants in period, weighted average grant date fair value (in dollars per share)		$ 9.43
Options, grants in period, weighted average exercise price (in dollars per share)		$ 78.05
Options, outstanding (in shares)	23	23		23
Options, outstanding, weighted average exercise price (in dollars per share)	$ 73.10	$ 73.10		$ 73.10
Options, outstanding, weighted average remaining contractual term (in years)	3 years 11 months 23 days
Employee Stock Option
Compensation
Stock-based compensation expense		$ 14	17	$ 34	39
Restricted Stock Units (RSUs)
Compensation
Stock-based compensation expense		$ 39	$ 33	$ 74	$ 68
Equity instruments other than options, grants in period (in shares)		3
Equity instruments other than options, grants in period, weighted average grant date fair value (in dollars per share)		$ 78.05
Equity instruments other than options, nonvested (in shares)	6	6		6
Equity instruments other than options, nonvested, weighted average grant date fair value (in dollars per share)	$ 86.79	$ 86.79		$ 86.79