Equity and Equity Compensation - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Capital stock, shares authorized	2,000,000,000.0
Common stock, shares authorized	1,500,000,000	1,500,000,000
Common stock, par value (usd per share)	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	500,000,000
Treasury stock acquired, weighted average cost per share (usd per share)	$ 21.19	$ 19.40
Number of shares authorized for issuance under the Plan (shares)	163,000,000
Capital shares reserved for future issuance (shares)	30,000,000
Share-based compensation	$ 108	$ 105	$ 76
Compensation cost not yet recognized	$ 82
Unvested restricted stock awards (shares)	2,600,000
Outstanding stock option awards (shares)	1,900,000
Outstanding stock option awards exercisable, weighted average exercise price (usd per share)	$ 38.59
Number of exercisable stock option awards (shares)	771,000
Excess tax benefits	$ 21	$ 33