Basis of Presentation and Significant Accounting Policies - Additional Information (Detail) - USD ($)	3 Months Ended			6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018	Jan. 01, 2019	Dec. 31, 2018	May 08, 2018
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Loss on asset disposals	$ 102,000,000	$ 1,000,000		$ 103,000,000	$ 1,000,000
Cost of operations	1,959,000,000	1,498,000,000		3,987,000,000	1,974,000,000
Selling, general and administrative expenses	77,000,000	75,000,000		149,000,000	124,000,000
Operating lease right-of-use assets	383,000,000			383,000,000
Current portion of long-term lease obligations	96,000,000			96,000,000			$ 8,000,000
Long-term lease obligations	$ 379,000,000			379,000,000			$ 66,000,000
Senior secured long-term borrowing								$ 2,260,000,000
Interest Rate Swap [Member] | Designated as Hedging Instrument [Member] | Cash Flow Hedging [Member]
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Interest rate derivatives								$ 1,940,000,000
ASU 2016-02 [Member]
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Operating lease right-of-use assets						$ 424,000,000
Current portion of long-term lease obligations						101,000,000
Long-term lease obligations						$ 342,000,000
Other Operating Expense [Member]
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Loss on asset disposals		$ (1,000,000)			(1,000,000)
Post-Combination Bid and Proposal Costs [Member]
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Cost of operations				$ 46,000,000	$ 17,000,000
Pre-Combination Bid and Proposal Costs [Member]
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Selling, general and administrative expenses			$ 10,000,000