Exit Activities and Discontinued Operations - Narrative (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended		18 Months Ended
	Dec. 31, 2021	Jun. 30, 2021	Jun. 30, 2020	Mar. 31, 2021
Discontinued Operations, Held-for-sale | EnerBank | Forecast
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from divestiture of businesses	$ 960
Retention Benefits | D.E. Karn Generating Complex
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Expected cost		$ 35
Retention and severance costs		0	$ 7	$ 16
Costs incurred and capitalized		0	$ 1
Retention Benefits | D.E. Karn Generating Complex | Retention Incentive Program
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Regulatory asset		$ 4
Retention Benefits | D.E. Karn Generating Complex | Property, Plant and Equipment
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Costs incurred and capitalized				$ 3