Stockholder's Equity - Changes in the Number of Shares Outstanding and Treasury Shares Held by the Company (Details) - shares shares in Millions	12 Months Ended
	Dec. 31, 2018	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