Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Deferred tax liabilities
Property related	$ 1,036	$ 969
Pension and postretirement benefits	111	105
Total deferred tax liabilities	1,147	1,074
Deferred tax assets
Loss and credit carryforwards	243	146
Medical benefits	27	24
Insurance reserves	16	17
Pension and postretirement benefits	63	63
Capitalized energy conservation assistance costs	17	16
Other	23	9
Total deferred tax assets	389	275
Total deferred tax liability, net	$ 758	$ 799