Summary of Significant Accounting Policies and Other Matters - Reconciliation of Cash, Temporary Investments and Restricted Cash (Details) $ in Millions	Sep. 30, 2023 USD ($) MWh	Dec. 31, 2022 USD ($)	Sep. 30, 2022 USD ($)
Cash and Cash Equivalents [Line Items]
Cash and temporary cash investments	$ 539	$ 1,282	$ 78
Restricted cash	6		163
Total cash, temporary cash investments and restricted cash	$ 545		241
Electric Energy (MWh)
Cash and Cash Equivalents [Line Items]
Notional amount | MWh	30,376,045
Broken Bow II | Electric Energy (MWh) | Clean Energy Businesses
Cash and Cash Equivalents [Line Items]
Notional amount | MWh	75
Subsidiaries
Cash and Cash Equivalents [Line Items]
Cash and temporary cash investments	$ 20		25
Restricted cash	0		0
Total cash, temporary cash investments and restricted cash	20		25
Clean Energy Businesses | Cash Collateral Held for Project Finance Agreements
Cash and Cash Equivalents [Line Items]
Restricted cash	$ 5		$ 163