Exit Activities - Narrative (Details) - D.E. Karn Generating Complex $ in Millions	3 Months Ended	6 Months Ended
Mar. 31, 2020 USD ($)	Mar. 31, 2020 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Expected cost	$ 35	$ 35
Retention Benefits
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Retention costs	$ 4	7
Property, Plant and Equipment \| Retention Benefits
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cost capitalized		$ 1

Amount of expenses associated with exit or disposal activities pursuant to an authorized plan. Excludes expenses related to a discontinued operation or an asset retirement obligation.

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