Stock-Based Compensation - Narrative (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Jul. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation cost	$ 121	$ 37
Vesting period	3 years
Options outstanding, weighted average remaining contractual term	4 years 8 months 10 days
Options exercisable, weighted average remaining contractual term	3 years
Options vested (in shares)	505
Unrecognized compensation cost, unvested	$ 18
Stock option exercised, intrinsic value	6
Options outstanding, intrinsic value	$ 1
Share price (in dollars per share)	$ 21.50
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost, unvested	$ 166
Unvested, weighted average period	1 year 10 months 23 days
Intrinsic value, vested	$ 41
Intrinsic value, outstanding	148
Fair value options vested in period	$ 45
Shares issued in period (in shares)	5,269
Granted, weighted average grant date fair value (in dollars per share)	$ 35.47
Unvested and outstanding (in shares)	6,882	3,286
Performance Share Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost, unvested	$ 23
Unvested, weighted average period	2 years 2 months 13 days
Intrinsic value, vested	$ 20
Stock-based compensation, service period	3 years
Shares issued in period (in shares)	952
Granted, weighted average grant date fair value (in dollars per share)	$ 35.13
Unvested and outstanding (in shares)	927
Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options outstanding, maximum weighted average contractual term	9 years 7 months 4 days
Unvested, weighted average period	1 year 9 months 19 days
Long-Term Inventive Plan (LTI Plan) | Class A
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized (in shares)	46,200		57,400