Benefit Plans and Other Postretirement Benefits - Net Benefit Costs and Funded Status (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Pension Benefits
Annual periodic pension cost
Service cost benefits earned	$ 7	$ 9	$ 10
Interest cost on benefit obligation	41	27	38
Expected return on plan assets	(47)	(66)	(61)
Amortization of unrecognized net loss	3	1	5
Curtailment loss	14	2	0
Net periodic benefit cost/(credit)	18	(27)	(8)
Pension and other post retirement benefit obligations
Benefit obligation at January 1	1,452	1,489
Acquired benefit obligation from Direct Energy	0	74
Service cost	7	9	10
Interest cost	41	27	38
Actuarial gain	(289)	(55)
Employee and retiree contributions	0	0
Curtailment loss	0	0
Benefit payments	(171)	(93)
Foreign exchange translation	(4)	1
Benefit obligation at December 31	1,036	1,452	1,489
Fair value of plan assets for pension and other post retirement benefit
Fair value of plan assets at January 1	1,336	1,272
Acquired fair value of plan assets from Direct Energy	0	64
Actual return on plan assets	(317)	85
Employee and retiree contributions	0	0
Employer contributions	0	7
Benefit payments	(171)	(93)
Foreign exchange translation	(4)	1
Fair value of plan assets at December 31	844	1,336	1,272
Funded status at December 31 — excess of obligation over assets	(192)	(116)
Other Postretirement Benefits Plan
Annual periodic pension cost
Service cost benefits earned	0	0
Interest cost on benefit obligation	2	2	3
Amortization of unrecognized prior service cost	(8)	(10)	(14)
Amortization of unrecognized net loss	2	1	1
Curtailment loss	0	1	0
Net periodic benefit cost/(credit)	(4)	(6)	(10)
Pension and other post retirement benefit obligations
Benefit obligation at January 1	105	90
Acquired benefit obligation from Direct Energy	0	19
Service cost	0	0
Interest cost	2	2	3
Actuarial gain	(11)	0
Employee and retiree contributions	3	3
Curtailment loss	0	1
Benefit payments	(15)	(10)
Foreign exchange translation	0	0
Benefit obligation at December 31	84	105	90
Fair value of plan assets for pension and other post retirement benefit
Fair value of plan assets at January 1	0	0
Acquired fair value of plan assets from Direct Energy	0	0
Actual return on plan assets	0	0
Employee and retiree contributions	3	3
Employer contributions	12	7
Benefit payments	(15)	(10)
Foreign exchange translation	0	0
Fair value of plan assets at December 31	0	0	$ 0
Funded status at December 31 — excess of obligation over assets	$ (84)	$ (105)

Amount of increase (decrease) in plan assets of defined benefit plan from actual return (loss) determined by change in fair value of plan assets adjusted for contributions, benefit payments, and other expenses.

Name:	us-gaap_DefinedBenefitPlanActualReturnOnPlanAssets
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of gain (loss) from change in actuarial assumptions which (increases) decreases benefit obligation of defined benefit plan. Assumptions include, but are not limited to, interest, mortality, employee turnover, salary, and temporary deviation from substantive plan.