Goodwill and Identifiable Intangible Assets and Liabilities - Schedule of Identifiable Intangible Assets and Liabilities Reported in the Balance Sheet (Details) - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
Finite-Lived and Indefinite-Lived Intangible [Line Items]
Gross Carrying Amount	$ 3,579	$ 3,513
Accumulated Amortization	2,823	2,641
Net	756	872
Total identifiable intangible assets	2,097	2,213
Total identifiable intangible liabilities	141	155
Retail trade names (not subject to amortization)
Finite-Lived and Indefinite-Lived Intangible [Line Items]
Gross carrying amount, unamortized intangibles	1,341	1,341
Retail customer relationships
Finite-Lived and Indefinite-Lived Intangible [Line Items]
Gross Carrying Amount	2,173	2,173
Accumulated Amortization	2,044	1,977
Net	129	196
Software and other technology-related assets
Finite-Lived and Indefinite-Lived Intangible [Line Items]
Gross Carrying Amount	566	601
Accumulated Amortization	347	293
Net	219	308
Retail and wholesale contracts
Finite-Lived and Indefinite-Lived Intangible [Line Items]
Gross Carrying Amount	503	503
Accumulated Amortization	410	353
Net	93	150
Long-term service agreements
Finite-Lived and Indefinite-Lived Intangible [Line Items]
Gross Carrying Amount	18	18
Accumulated Amortization	6	5
Net	12	13
Total identifiable intangible liabilities	101	108
Other identifiable intangible assets
Finite-Lived and Indefinite-Lived Intangible [Line Items]
Gross Carrying Amount	319	218
Accumulated Amortization	16	13
Net	303	205
Wholesale power and fuel purchase contracts
Finite-Lived and Indefinite-Lived Intangible [Line Items]
Total identifiable intangible liabilities	$ 40	$ 47