Revenue - Schedule of Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	$ 4,250	$ 3,159
Total revenues	3,933	3,054
Retail energy charge in ERCOT
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	1,986	1,702
Retail energy charge in Northeast/Midwest
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	1,039	663
Wholesale generation revenue from ISO/RTO
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	874	489
Capacity revenue from ISO/RTO
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	20	19
Revenue from other wholesale contracts
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	331	286
Transferable PTC revenues
Disaggregation of Revenue [Line Items]
Total revenues	2	2
Hedging revenues — realized
Disaggregation of Revenue [Line Items]
Total revenues	195	241
Hedging revenues — unrealized
Disaggregation of Revenue [Line Items]
Total revenues	(513)	(347)
Intangible amortization and other revenues
Disaggregation of Revenue [Line Items]
Total revenues	(1)	(1)
Intersegment sales
Disaggregation of Revenue [Line Items]
Total revenues	0	0
Total other revenues
Disaggregation of Revenue [Line Items]
Total revenues	(317)	(105)
Operating Segments
Disaggregation of Revenue [Line Items]
Total revenues	4,919	4,094
Operating Segments | Retail
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	3,025	2,365
Total revenues	3,168	2,494
Operating Segments | Texas
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	207	172
Total revenues	210	459
Operating Segments | Texas | Commodity contracts unrealized (gain) loss in operating revenues
Disaggregation of Revenue [Line Items]
Unrealized gain (loss) on derivatives affiliated	(883)	(490)
Operating Segments | East
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	920	477
Total revenues	1,380	856
Operating Segments | East | Commodity contracts unrealized (gain) loss in operating revenues
Disaggregation of Revenue [Line Items]
Unrealized gain (loss) on derivatives affiliated	(271)	(291)
Operating Segments | West
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	94	136
Total revenues	157	276
Operating Segments | West | Commodity contracts unrealized (gain) loss in operating revenues
Disaggregation of Revenue [Line Items]
Unrealized gain (loss) on derivatives affiliated	1
Operating Segments | Asset Closure
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	4	9
Total revenues	4	9
Operating Segments | Retail energy charge in ERCOT | Retail
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	1,986	1,702
Operating Segments | Retail energy charge in ERCOT | Texas
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
Operating Segments | Retail energy charge in ERCOT | East
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
Operating Segments | Retail energy charge in ERCOT | West
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
Operating Segments | Retail energy charge in ERCOT | Asset Closure
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
Operating Segments | Retail energy charge in Northeast/Midwest | Retail
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	1,039	663
Operating Segments | Retail energy charge in Northeast/Midwest | Texas
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
Operating Segments | Retail energy charge in Northeast/Midwest | East
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
Operating Segments | Retail energy charge in Northeast/Midwest | West
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
Operating Segments | Retail energy charge in Northeast/Midwest | Asset Closure
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
Operating Segments | Wholesale generation revenue from ISO/RTO | Retail
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
Operating Segments | Wholesale generation revenue from ISO/RTO | Texas
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	78	68
Operating Segments | Wholesale generation revenue from ISO/RTO | East
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	770	333
Operating Segments | Wholesale generation revenue from ISO/RTO | West
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	26	79
Operating Segments | Wholesale generation revenue from ISO/RTO | Asset Closure
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	9
Operating Segments | Capacity revenue from ISO/RTO | Retail
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
Operating Segments | Capacity revenue from ISO/RTO | Texas
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
Operating Segments | Capacity revenue from ISO/RTO | East
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	20	19
Net capacity sold		40
Net capacity purchased		21
Operating Segments | Capacity revenue from ISO/RTO | East | Commodity contracts unrealized (gain) loss in operating revenues
Disaggregation of Revenue [Line Items]
Net capacity sold	73
Net capacity purchased	53
Operating Segments | Capacity revenue from ISO/RTO | East | Fuel, purchased power costs, and delivery fees/Depreciation and amortization
Disaggregation of Revenue [Line Items]
Net capacity sold		(2)
Net capacity purchased		7
Operating Segments | Capacity revenue from ISO/RTO | West
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
Operating Segments | Capacity revenue from ISO/RTO | Asset Closure
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
Operating Segments | Revenue from other wholesale contracts | Retail
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
Operating Segments | Revenue from other wholesale contracts | Texas
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	129	104
Operating Segments | Revenue from other wholesale contracts | East
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	130	125
Operating Segments | Revenue from other wholesale contracts | West
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	68	57
Operating Segments | Revenue from other wholesale contracts | Asset Closure
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	4	0
Operating Segments | Transferable PTC revenues | Retail
Disaggregation of Revenue [Line Items]
Total revenues	0	0
Operating Segments | Transferable PTC revenues | Texas
Disaggregation of Revenue [Line Items]
Total revenues	2	2
Operating Segments | Transferable PTC revenues | East
Disaggregation of Revenue [Line Items]
Total revenues	0	0
Operating Segments | Transferable PTC revenues | West
Disaggregation of Revenue [Line Items]
Total revenues	0	0
Operating Segments | Transferable PTC revenues | Asset Closure
Disaggregation of Revenue [Line Items]
Total revenues	0	0
Operating Segments | Hedging revenues — realized | Retail
Disaggregation of Revenue [Line Items]
Total revenues	274	278
Operating Segments | Hedging revenues — realized | Texas
Disaggregation of Revenue [Line Items]
Total revenues	(27)	(110)
Operating Segments | Hedging revenues — realized | East
Disaggregation of Revenue [Line Items]
Total revenues	(78)	74
Operating Segments | Hedging revenues — realized | West
Disaggregation of Revenue [Line Items]
Total revenues	26	3
Operating Segments | Hedging revenues — realized | Asset Closure
Disaggregation of Revenue [Line Items]
Total revenues	0	(4)
Operating Segments | Hedging revenues — unrealized | Retail
Disaggregation of Revenue [Line Items]
Total revenues	(157)	(155)
Operating Segments | Hedging revenues — unrealized | Texas
Disaggregation of Revenue [Line Items]
Total revenues	(143)	(132)
Operating Segments | Hedging revenues — unrealized | East
Disaggregation of Revenue [Line Items]
Total revenues	(250)	(200)
Operating Segments | Hedging revenues — unrealized | West
Disaggregation of Revenue [Line Items]
Total revenues	36	136
Operating Segments | Hedging revenues — unrealized | Asset Closure
Disaggregation of Revenue [Line Items]
Total revenues	1	4
Operating Segments | Intangible amortization and other revenues | Retail
Disaggregation of Revenue [Line Items]
Total revenues	0	0
Operating Segments | Intangible amortization and other revenues | Texas
Disaggregation of Revenue [Line Items]
Total revenues	0	0
Operating Segments | Intangible amortization and other revenues | East
Disaggregation of Revenue [Line Items]
Total revenues	(1)	(1)
Operating Segments | Intangible amortization and other revenues | West
Disaggregation of Revenue [Line Items]
Total revenues	0	0
Operating Segments | Intangible amortization and other revenues | Asset Closure
Disaggregation of Revenue [Line Items]
Total revenues	0	0
Operating Segments | Intersegment sales | Retail
Disaggregation of Revenue [Line Items]
Total revenues	26	6
Operating Segments | Intersegment sales | Texas
Disaggregation of Revenue [Line Items]
Total revenues	171	527
Operating Segments | Intersegment sales | East
Disaggregation of Revenue [Line Items]
Total revenues	789	506
Operating Segments | Intersegment sales | West
Disaggregation of Revenue [Line Items]
Total revenues	1	1
Operating Segments | Intersegment sales | Asset Closure
Disaggregation of Revenue [Line Items]
Total revenues	(1)	0
Operating Segments | Total other revenues | Retail
Disaggregation of Revenue [Line Items]
Total revenues	143	129
Operating Segments | Total other revenues | Texas
Disaggregation of Revenue [Line Items]
Total revenues	3	287
Operating Segments | Total other revenues | East
Disaggregation of Revenue [Line Items]
Total revenues	460	379
Operating Segments | Total other revenues | West
Disaggregation of Revenue [Line Items]
Total revenues	63	140
Operating Segments | Total other revenues | Asset Closure
Disaggregation of Revenue [Line Items]
Total revenues	0	0
Eliminations
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
Total revenues	(986)	(1,040)
Eliminations | Retail energy charge in ERCOT
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
Eliminations | Retail energy charge in Northeast/Midwest
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
Eliminations | Wholesale generation revenue from ISO/RTO
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
Eliminations | Capacity revenue from ISO/RTO
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
Eliminations | Revenue from other wholesale contracts
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0
Eliminations | Transferable PTC revenues
Disaggregation of Revenue [Line Items]
Total revenues	0	0
Eliminations | Hedging revenues — realized
Disaggregation of Revenue [Line Items]
Total revenues	0	0
Eliminations | Hedging revenues — unrealized
Disaggregation of Revenue [Line Items]
Total revenues	0	0
Eliminations | Intangible amortization and other revenues
Disaggregation of Revenue [Line Items]
Total revenues	0	0
Eliminations | Intersegment sales
Disaggregation of Revenue [Line Items]
Total revenues	(986)	(1,040)
Eliminations | Total other revenues
Disaggregation of Revenue [Line Items]
Total revenues	$ (986)	$ (1,040)