Goodwill and Other Intangible Assets - Changes in the Carrying Amount of Goodwill by Reporting Segment (Parenthetical) (Detail) - USD ($) $ in Millions	3 Months Ended						12 Months Ended
	Dec. 31, 2019		Sep. 30, 2019		Dec. 31, 2018		Dec. 31, 2019		Dec. 31, 2018
Goodwill And Intangible Assets Disclosure [Abstract]
Cumulative impairment charges	$ 60	[1]	$ 1,370	[1]	$ 2,168	[2],[3]	$ 1,430	[4]	$ 2,168	[4]

[1] 2019—represents impairment of goodwill associated with our NCSA and EARC reporting units, resulting from our interim and annual impairment assessment. See Note 9, Goodwill and Other Intangible Assets, for further discussion.

[2] 2018—represents impairment of goodwill associated with our NCSA, EARC, APAC and Technology reporting units, resulting from our annual impairment assessment.

[3] Results in the second, third and fourth quarters of 2018 reflect impacts of the Combination from the Combination Date.

[4] Represents impairment of goodwill associated with our NCSA and EARC reporting units in 2019 and our NCSA, EARC, APAC and Technology reporting units in 2018. See Note 9, Goodwill and Other Intangible Assets, for further discussion. The goodwill impairment values are included within the applicable operating group’s Operating loss.