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Impairments (Details) - USD ($) $ in Millions	3 Months Ended
Impairments (Details) - USD ($) $ in Millions	Jun. 30, 2021	Sep. 30, 2020	Mar. 31, 2020	Sep. 30, 2019
Petra Nova
Schedule of Equity Method Investments [Line Items]
Impairment losses			$ 18
Letters of credit issued				$ 12
East
Schedule of Equity Method Investments [Line Items]
Property plant and equipment impairment loss	$ 271
Goodwill impairment loss	$ 35
West/Services/Other \| Disposal Group, Held-for-sale, Not Discontinued Operations \| Home Solar
Schedule of Equity Method Investments [Line Items]
Adjustment to carrying amount of assets and liabilities		$ 29