Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Deferred tax assets:
Deferred compensation, accrued vacation and other reserves	$ 114	$ 79
Difference between book and tax basis of property	436	357
Pension and other postretirement benefits	65	86
Equity compensation	7	10
Bad debt reserve	168	16
Derivatives, net	0	11
U.S. Federal net operating loss carryforwards	1,773	2,117
Foreign net operating loss carryforwards	112	102
State net operating loss carryforwards	328	351
Federal and state tax credit carryforwards	384	384
Federal benefit on state uncertain tax positions	3	4
Interest disallowance carryforward per §163(j) of the Tax Act	6	4
Inventory obsolescence	9	6
Other	15	10
Total deferred tax assets	3,420	3,537
Deferred tax liabilities:
Emissions allowances	20	21
Derivatives, net	591	0
Goodwill	40	29
Intangibles amortization (excluding goodwill)	363	2
Equity method investments	62	156
Convertible Debt	14	16
Total deferred tax liabilities	1,090	224
Total deferred tax assets less deferred tax liabilities	2,330	3,313
Valuation allowance	(248)	(266)
Net deferred tax asset	2,082	3,047
NRG's net deferred tax position
Deferred tax asset	2,155	3,066
Deferred tax liability	(73)	(19)
Net deferred tax asset	$ 2,082	$ 3,047