Income Taxes - Components of Deferred Tax Liabilities and Deferred Tax Assets (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Deferred Tax Liabilities
Property, plant and equipment and investments	$ (3,810)	$ (3,743)
Other	(255)	(257)
Total Deferred Tax Liabilities	(4,065)	(4,000)
Deferred Tax Assets
Net operating loss carryforwards	5,767	3,852
Tax credit carryforwards	164	188
Property, plant and equipment and investments	834	981
Accrued compensation, deferred credits and other liabilities	526	492
Asset retirement obligations	1,077	1,220
Other	62	165
Total Deferred Tax Assets	8,430	6,898
Valuation allowances	(5,450)	(1,579)
Total deferred tax assets, net of valuation allowances	2,980	5,319
Net Deferred Tax Liabilities	$ (1,085)
Net Deferred Tax Assets		$ 1,319