Exit Activities - Narrative (Details) - D.E. Karn Generating Complex $ in Millions	3 Months Ended	6 Months Ended	9 Months Ended
	Jun. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Expected cost	$ 35	$ 35	$ 35
Retention Benefits
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Retention costs	$ 3	7	11
Costs incurred and capitalized		$ 1
Property, Plant and Equipment | Retention Benefits
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Costs incurred and capitalized			$ 1