Stockholders' Equity and Equity-Based Incentive Plans - Changes in the Number of Shares Outstanding and Treasury Shares Held by the Company (Detail) - shares shares in Millions	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Shares Outstanding [Abstract]
Beginning balance	181	95
Common stock issued	2	2
Shares issued in the Combination (Note 3, Business Combination)		85
Purchase of common stock	(1)	(1)
Ending balance	182	181
Shares Held as Treasury Shares [Abstract]
Beginning balance	3	3
Purchase of common stock	1	1
Retirement of common stock	(1)	(1)
Ending balance	3	3
Common stock, shares issued	185	183	183