Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Millions		Dec. 31, 2023	Dec. 31, 2022
Deferred tax liabilities
Property related		$ 1,227	$ 1,318
Deferred fuel		23	133
Pension and postretirement benefits		100	111
Insurance reserves		0	15
Total deferred tax liabilities		1,350	1,577
Deferred tax assets
Loss and credit carryforwards	[1]	383	408
Medical benefits		19	24
Insurance reserves		1	0
Pension and postretirement benefits		49	57
Capitalized energy conservation assistance costs		0	23
Other		18	20
Total deferred tax assets		470	532
Total deferred tax liability, net		$ 880	$ 1,045

[1] Deferred tax assets for net operating loss and tax credit carryforwards have been reduced by unrecognized tax benefits of $10 million and $9 million at December 31, 2023 and 2022, respectively.