Revenue - Schedule of Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	$ 4,778	$ 4,341	$ 12,781	$ 11,099
Total revenues	4,971	6,288	13,154	13,187
Retail energy charge in ERCOT
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	2,698	2,500	6,890	6,241
Retail energy charge in Northeast/Midwest
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	1,054	1,051	2,886	2,705
Wholesale generation revenue from ISO/RTO
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	683	520	2,031	1,290
Capacity revenue from ISO/RTO
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	79	18	129	54
Revenue from other wholesale contracts
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	264	252	845	809
Transferable PTC revenues
Disaggregation of Revenue [Line Items]
Total revenues	145	4	151	9
Hedging revenues — realized
Disaggregation of Revenue [Line Items]
Total revenues	(108)	(29)	514	498
Hedging revenues — unrealized
Disaggregation of Revenue [Line Items]
Total revenues	162	1,960	(301)	1,571
Business interruption insurance proceeds
Disaggregation of Revenue [Line Items]
Total revenues	1		22
Intangible amortization and other revenues
Disaggregation of Revenue [Line Items]
Total revenues	(7)	12	(13)	10
Intersegment sales
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Total other revenues
Disaggregation of Revenue [Line Items]
Total revenues	193	1,947	373	2,088
Operating Segments
Disaggregation of Revenue [Line Items]
Total revenues	7,855	10,591	19,619	19,808
Operating Segments | Retail
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	3,752	3,551	9,776	8,946
Total revenues	4,139	4,251	10,839	9,913
Operating Segments | Texas
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	212	215	569	603
Total revenues	1,799	4,244	3,797	4,924
Operating Segments | Texas | Commodity contracts unrealized gain (loss) in operating revenues
Disaggregation of Revenue [Line Items]
Unrealized gain (loss) on derivatives affiliated	(28)	1,527	(93)	605
Operating Segments | East
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	723	465	2,177	1,210
Total revenues	1,750	1,853	4,610	4,241
Operating Segments | East | Commodity contracts unrealized gain (loss) in operating revenues
Disaggregation of Revenue [Line Items]
Unrealized gain (loss) on derivatives affiliated	4	55	(103)	(123)
Operating Segments | West
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	89	98	251	311
Total revenues	165	232	347	701
Operating Segments | West | Commodity contracts unrealized gain (loss) in operating revenues
Disaggregation of Revenue [Line Items]
Unrealized gain (loss) on derivatives affiliated		1		3
Operating Segments | Asset Closure
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	11	5	28
Total revenues	2	11	26	29
Operating Segments | Retail energy charge in ERCOT | Retail
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	2,698	2,500	6,890	6,241
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
Disaggregation of Revenue [Line Items]
Acquired revenue, duration				7 months
Operating Segments | Retail energy charge in Northeast/Midwest | Retail
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	1,054	1,051	2,886	$ 2,705
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	112	122	231	278
Operating Segments | Wholesale generation revenue from ISO/RTO | East
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	543	347	1,725	844
Operating Segments | Wholesale generation revenue from ISO/RTO | West
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	28	50	75	164
Operating Segments | Wholesale generation revenue from ISO/RTO | Asset Closure
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	1	0	4
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	79	18	129	54
Net capacity sold				94
Net capacity purchased				40
Operating Segments | Capacity revenue from ISO/RTO | East | Commodity contracts unrealized gain (loss) in operating revenues
Disaggregation of Revenue [Line Items]
Net capacity sold	270	30	477
Net capacity purchased	191	12	348
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		28		47
Net capacity purchased		44		88
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	100	93	338	325
Operating Segments | Revenue from other wholesale contracts | East
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	101	100	323	312
Operating Segments | Revenue from other wholesale contracts | West
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	61	48	176	147
Operating Segments | Revenue from other wholesale contracts | Asset Closure
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	10	5	24
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	145	4	151	9
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	396	373	1,040	927
Operating Segments | Hedging revenues — realized | Texas
Disaggregation of Revenue [Line Items]
Total revenues	(422)	(382)	(458)	(524)
Operating Segments | Hedging revenues — realized | East
Disaggregation of Revenue [Line Items]
Total revenues	(108)	(52)	(158)	35
Operating Segments | Hedging revenues — realized | West
Disaggregation of Revenue [Line Items]
Total revenues	26	35	90	68
Operating Segments | Hedging revenues — realized | Asset Closure
Disaggregation of Revenue [Line Items]
Total revenues	0	(3)	0	(8)
Operating Segments | Hedging revenues — unrealized | Retail
Disaggregation of Revenue [Line Items]
Total revenues	(43)	308	(59)	(3)
Operating Segments | Hedging revenues — unrealized | Texas
Disaggregation of Revenue [Line Items]
Total revenues	251	1,253	198	893
Operating Segments | Hedging revenues — unrealized | East
Disaggregation of Revenue [Line Items]
Total revenues	(97)	299	(446)	356
Operating Segments | Hedging revenues — unrealized | West
Disaggregation of Revenue [Line Items]
Total revenues	50	98	4	317
Operating Segments | Hedging revenues — unrealized | Asset Closure
Disaggregation of Revenue [Line Items]
Total revenues	1	2	2	8
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	1		22
Operating Segments | Intangible amortization and other revenues | Retail
Disaggregation of Revenue [Line Items]
Total revenues	0	1	0	0
Operating Segments | Intangible amortization and other revenues | Texas
Disaggregation of Revenue [Line Items]
Total revenues	0	0	(2)	0
Operating Segments | Intangible amortization and other revenues | East
Disaggregation of Revenue [Line Items]
Total revenues	(7)	(1)	(11)	(3)
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	1	0	1
Operating Segments | Intersegment sales | Retail
Disaggregation of Revenue [Line Items]
Total revenues	34	18	82	43
Operating Segments | Intersegment sales | Texas
Disaggregation of Revenue [Line Items]
Total revenues	1,613	3,154	3,339	3,943
Operating Segments | Intersegment sales | East
Disaggregation of Revenue [Line Items]
Total revenues	1,239	1,142	3,048	2,643
Operating Segments | Intersegment sales | West
Disaggregation of Revenue [Line Items]
Total revenues	0	1	2	5
Operating Segments | Intersegment sales | Asset Closure
Disaggregation of Revenue [Line Items]
Total revenues	0	0	(3)	0
Operating Segments | Total other revenues | Retail
Disaggregation of Revenue [Line Items]
Total revenues	387	700	1,063	967
Operating Segments | Total other revenues | Texas
Disaggregation of Revenue [Line Items]
Total revenues	1,587	4,029	3,228	4,321
Operating Segments | Total other revenues | East
Disaggregation of Revenue [Line Items]
Total revenues	1,027	1,388	2,433	3,031
Operating Segments | Total other revenues | West
Disaggregation of Revenue [Line Items]
Total revenues	76	134	96	390
Operating Segments | Total other revenues | Asset Closure
Disaggregation of Revenue [Line Items]
Total revenues	2	0	21	1
Eliminations
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	2	1	3	1
Total revenues	(2,884)	(4,303)	(6,465)	(6,621)
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	2	1	3	1
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	11	0	12
Eliminations | Intersegment sales
Disaggregation of Revenue [Line Items]
Total revenues	(2,886)	(4,315)	(6,468)	(6,634)
Eliminations | Total other revenues
Disaggregation of Revenue [Line Items]
Total revenues	$ (2,886)	$ (4,304)	$ (6,468)	$ (6,622)