Income Taxes - Additional Information (Detail) - USD ($)	Dec. 31, 2020	Dec. 31, 2019
Income Tax Examination [Line Items]
Gross deferred tax asset related to net operating loss carryforwards	$ 5,037,000,000	$ 4,733,000,000
Deferred tax asset related to foreign net operating loss carryforwards, net of valuation allowance	155,000,000
Valuation allowance against net deferred tax assets	5,391,000,000	4,734,000,000
Alternative minimum tax credit carryforwards	49,000,000
Other business credit carryforwards	83,000,000
Foreign tax credit carryforwards - Before valuation allowance	3,000,000
Unrecognized tax benefits that would impact effective income tax rate	16,000,000
Accrued interest and penalties	6,000,000	$ 7,000,000
Minimum
Income Tax Examination [Line Items]
Unrecognized tax benefits decrease reasonably possible	0
Maximum
Income Tax Examination [Line Items]
Unrecognized tax benefits decrease reasonably possible	41,000,000
U.S. Federal
Income Tax Examination [Line Items]
Gross deferred tax asset related to net U.S. federal operating loss carryforwards	3,277,000,000
U.S. Federal | Midstream
Income Tax Examination [Line Items]
Valuation allowance against net deferred tax assets	3,000,000
U.S. State
Income Tax Examination [Line Items]
Gross deferred tax asset related to net operating loss carryforwards for various U.S. states	639,000,000
U.S. State | Midstream
Income Tax Examination [Line Items]
Valuation allowance against net deferred tax assets	1,000,000
Foreign
Income Tax Examination [Line Items]
Gross deferred tax asset related to foreign net operating loss carryforwards	$ 1,121,000,000