Stockholders' Equity and Equity-Based Incentive Plans - Changes in the Number of Shares Outstanding and Treasury Shares Held by the Company (Details) - shares shares in Millions	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Shares Outstanding [Abstract]
Beginning balance	95	80
Common stock issued	2	15
Shares issued in the Combination (Note 3, Business Combination)	85
Purchase of common stock	(1)
Ending balance	181	95
Shares Held as Treasury Shares [Abstract]
Beginning balance	3	3
Purchase of common stock	1
Retirement of common stock	(1)
Ending balance	3	3
Common stock, shares issued	183	98	98