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	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Shares Outstanding [Abstract]
Beginning balance	181	95
Common stock issued	2	1
Purchase of common stock	(1)
Ending balance	182	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	184	98	183