Income Taxes - Components of Deferred Tax Liabilities and Deferred Tax Assets (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Deferred Tax Liabilities
Property, plant and equipment and investments	$ (1,318)	$ (853)
Other	(45)	(77)
Total Deferred Tax Liabilities	(1,363)	(930)
Deferred Tax Assets
Net operating loss carryforwards	4,733	4,239
Tax credit carryforwards	66	134
Property, plant and equipment and investments	206	416
Accrued compensation, deferred credits and other liabilities	179	232
Asset retirement obligations	261	225
Other	317	161
Total Deferred Tax Assets	5,762	5,407
Valuation allowances	(4,734)	(4,877)
Total deferred tax assets, net of valuation allowances	1,028	530
Net Deferred Tax Assets (Liabilities)	$ (335)	$ (400)