Revenue - Schedule of Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	$ 3,753	$ 3,599	$ 8,003	$ 6,758
Total revenues	4,250	3,845	8,183	6,899
Retail energy charge in ERCOT
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	2,206	2,039	4,192	3,741
Retail energy charge in Northeast/Midwest
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	793	991	1,832	1,654
Wholesale generation revenue from ISO/RTO
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	474	281	1,348	770
Capacity revenue from ISO/RTO
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	30	17	50	36
Revenue from other wholesale contracts
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	250	271	581	557
Transferable PTC revenues
Disaggregation of Revenue [Line Items]
Total revenues	4	3	6	5
Hedging revenues — realized
Disaggregation of Revenue [Line Items]
Total revenues	427	286	622	527
Hedging revenues — unrealized
Disaggregation of Revenue [Line Items]
Total revenues	50	(42)	(463)	(389)
Business interruption insurance proceeds
Disaggregation of Revenue [Line Items]
Total revenues	21		21
Intangible amortization and other revenues
Disaggregation of Revenue [Line Items]
Total revenues	(5)	(1)	(6)	(2)
Intersegment sales
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Total other revenues
Disaggregation of Revenue [Line Items]
Total revenues	497	246	180	141
Operating Segments
Disaggregation of Revenue [Line Items]
Total revenues	6,845	5,123	11,764	9,217
Operating Segments | Retail
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	2,999	3,030	6,024	5,395
Total revenues	3,532	3,168	6,700	5,662
Operating Segments | Texas
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	150	216	357	388
Total revenues	1,788	221	1,998	680
Operating Segments | Texas | Commodity contracts unrealized (gain) loss in operating revenues
Disaggregation of Revenue [Line Items]
Unrealized gain (loss) on derivatives affiliated	817	(432)	(65)	(922)
Operating Segments | East
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	534	268	1,454	745
Total revenues	1,480	1,532	2,860	2,388
Operating Segments | East | Commodity contracts unrealized (gain) loss in operating revenues
Disaggregation of Revenue [Line Items]
Unrealized gain (loss) on derivatives affiliated	164	113	(107)	(178)
Operating Segments | West
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	68	77	162	213
Total revenues	25	193	182	469
Operating Segments | West | Commodity contracts unrealized (gain) loss in operating revenues
Disaggregation of Revenue [Line Items]
Unrealized gain (loss) on derivatives affiliated		2
Operating Segments | Asset Closure
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	1	8	5	17
Total revenues	20	9	24	18
Operating Segments | Retail energy charge in ERCOT | Retail
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	2,206	2,039	4,192	3,741
Operating Segments | Retail energy charge in ERCOT | Texas
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
Operating Segments | Retail energy charge in ERCOT | East
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
Operating Segments | Retail energy charge in ERCOT | West
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
Operating Segments | Retail energy charge in ERCOT | Asset Closure
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
Operating Segments | Retail energy charge in Northeast/Midwest | Retail
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	793	991	1,832	1,654
Operating Segments | Retail energy charge in Northeast/Midwest | Texas
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
Operating Segments | Retail energy charge in Northeast/Midwest | East
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
Operating Segments | Retail energy charge in Northeast/Midwest | West
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	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	0	0
Operating Segments | Wholesale generation revenue from ISO/RTO | Retail
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
Operating Segments | Wholesale generation revenue from ISO/RTO | Texas
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	41	88	119	156
Operating Segments | Wholesale generation revenue from ISO/RTO | East
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	412	164	1,182	497
Operating Segments | Wholesale generation revenue from ISO/RTO | West
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	21	35	47	114
Operating Segments | Wholesale generation revenue from ISO/RTO | Asset Closure
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	(6)	0	3
Operating Segments | Capacity revenue from ISO/RTO | Retail
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
Operating Segments | Capacity revenue from ISO/RTO | Texas
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
Operating Segments | Capacity revenue from ISO/RTO | East
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	30	17	50	36
Net capacity sold		24		64
Net capacity purchased		7		28
Operating Segments | Capacity revenue from ISO/RTO | East | Commodity contracts unrealized (gain) loss in operating revenues
Disaggregation of Revenue [Line Items]
Net capacity sold	134		207
Net capacity purchased	104		157
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		21		19
Net capacity purchased		37		44
Operating Segments | Capacity revenue from ISO/RTO | West
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
Operating Segments | Capacity revenue from ISO/RTO | Asset Closure
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
Operating Segments | Revenue from other wholesale contracts | Retail
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
Operating Segments | Revenue from other wholesale contracts | Texas
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	109	128	238	232
Operating Segments | Revenue from other wholesale contracts | East
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	92	87	222	212
Operating Segments | Revenue from other wholesale contracts | West
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	47	42	115	99
Operating Segments | Revenue from other wholesale contracts | Asset Closure
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	1	14	5	14
Operating Segments | Transferable PTC revenues | Retail
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Operating Segments | Transferable PTC revenues | Texas
Disaggregation of Revenue [Line Items]
Total revenues	4	3	6	5
Operating Segments | Transferable PTC revenues | East
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Operating Segments | Transferable PTC revenues | West
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Operating Segments | Transferable PTC revenues | Asset Closure
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Operating Segments | Hedging revenues — realized | Retail
Disaggregation of Revenue [Line Items]
Total revenues	370	276	644	554
Operating Segments | Hedging revenues — realized | Texas
Disaggregation of Revenue [Line Items]
Total revenues	(9)	(32)	(36)	(142)
Operating Segments | Hedging revenues — realized | East
Disaggregation of Revenue [Line Items]
Total revenues	28	13	(50)	87
Operating Segments | Hedging revenues — realized | West
Disaggregation of Revenue [Line Items]
Total revenues	38	30	64	33
Operating Segments | Hedging revenues — realized | Asset Closure
Disaggregation of Revenue [Line Items]
Total revenues	0	(1)	0	(5)
Operating Segments | Hedging revenues — unrealized | Retail
Disaggregation of Revenue [Line Items]
Total revenues	141	(156)	(16)	(311)
Operating Segments | Hedging revenues — unrealized | Texas
Disaggregation of Revenue [Line Items]
Total revenues	90	(228)	(53)	(360)
Operating Segments | Hedging revenues — unrealized | East
Disaggregation of Revenue [Line Items]
Total revenues	(99)	257	(349)	57
Operating Segments | Hedging revenues — unrealized | West
Disaggregation of Revenue [Line Items]
Total revenues	(82)	83	(46)	219
Operating Segments | Hedging revenues — unrealized | Asset Closure
Disaggregation of Revenue [Line Items]
Total revenues	0	2	1	6
Operating Segments | Business interruption insurance proceeds | Retail
Disaggregation of Revenue [Line Items]
Total revenues	0		0
Operating Segments | Business interruption insurance proceeds | Texas
Disaggregation of Revenue [Line Items]
Total revenues	0		0
Operating Segments | Business interruption insurance proceeds | East
Disaggregation of Revenue [Line Items]
Total revenues	0		0
Operating Segments | Business interruption insurance proceeds | West
Disaggregation of Revenue [Line Items]
Total revenues	0		0
Operating Segments | Business interruption insurance proceeds | Asset Closure
Disaggregation of Revenue [Line Items]
Total revenues	21		21
Operating Segments | Intangible amortization and other revenues | Retail
Disaggregation of Revenue [Line Items]
Total revenues	0	(1)	0	(1)
Operating Segments | Intangible amortization and other revenues | Texas
Disaggregation of Revenue [Line Items]
Total revenues	(2)	0	(2)	0
Operating Segments | Intangible amortization and other revenues | East
Disaggregation of Revenue [Line Items]
Total revenues	(3)	(1)	(4)	(2)
Operating Segments | Intangible amortization and other revenues | West
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Operating Segments | Intangible amortization and other revenues | Asset Closure
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Operating Segments | Intersegment sales | Retail
Disaggregation of Revenue [Line Items]
Total revenues	22	19	48	25
Operating Segments | Intersegment sales | Texas
Disaggregation of Revenue [Line Items]
Total revenues	1,555	262	1,726	789
Operating Segments | Intersegment sales | East
Disaggregation of Revenue [Line Items]
Total revenues	1,020	995	1,809	1,501
Operating Segments | Intersegment sales | West
Disaggregation of Revenue [Line Items]
Total revenues	1	3	2	4
Operating Segments | Intersegment sales | Asset Closure
Disaggregation of Revenue [Line Items]
Total revenues	(2)	0	(3)	0
Operating Segments | Total other revenues | Retail
Disaggregation of Revenue [Line Items]
Total revenues	533	138	676	267
Operating Segments | Total other revenues | Texas
Disaggregation of Revenue [Line Items]
Total revenues	1,638	5	1,641	292
Operating Segments | Total other revenues | East
Disaggregation of Revenue [Line Items]
Total revenues	946	1,264	1,406	1,643
Operating Segments | Total other revenues | West
Disaggregation of Revenue [Line Items]
Total revenues	(43)	116	20	256
Operating Segments | Total other revenues | Asset Closure
Disaggregation of Revenue [Line Items]
Total revenues	19	1	19	1
Eliminations
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	1	0	1	0
Total revenues	(2,595)	(1,278)	(3,581)	(2,318)
Eliminations | Retail energy charge in ERCOT
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
Eliminations | Retail energy charge in Northeast/Midwest
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
Eliminations | Wholesale generation revenue from ISO/RTO
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
Eliminations | Capacity revenue from ISO/RTO
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
Eliminations | Revenue from other wholesale contracts
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	1	0	1	0
Eliminations | Transferable PTC revenues
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Eliminations | Hedging revenues — realized
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Eliminations | Hedging revenues — unrealized
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Eliminations | Business interruption insurance proceeds
Disaggregation of Revenue [Line Items]
Total revenues	0		0
Eliminations | Intangible amortization and other revenues
Disaggregation of Revenue [Line Items]
Total revenues	0	1	0	1
Eliminations | Intersegment sales
Disaggregation of Revenue [Line Items]
Total revenues	(2,596)	(1,279)	(3,582)	(2,319)
Eliminations | Total other revenues
Disaggregation of Revenue [Line Items]
Total revenues	$ (2,596)	$ (1,278)	$ (3,582)	$ (2,318)