Earnings Per Share - Computation of Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Numerator:
Net income attributable to NOW Inc.	$ 35	$ 40	$ 100	$ 96
Less: net income attributable to participating securities	(1)	(1)	(2)	(1)
Net income attributable to NOW Inc. stockholders	$ 34	$ 39	$ 98	$ 95
Denominator:
Weighted average basic common shares outstanding	106,983,920	110,863,381	107,765,405	110,747,087
Effect of dilutive securities	1,134,399	569,398	1,074,137	363,754
Weighted average diluted common shares outstanding	108,118,319	111,432,779	108,839,542	111,110,841
Basic	$ 0.32	$ 0.35	$ 0.91	$ 0.85
Diluted	$ 0.32	$ 0.35	$ 0.9	$ 0.85