Regulatory and Rate Matters - TNMP Narrative (Details) - TNMP				9 Months Ended
	Apr. 05, 2022 USD ($)	Jul. 01, 2021 USD ($)	Apr. 05, 2021 USD ($)	Dec. 31, 2018 USD ($)	Mar. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	May 27, 2021 USD ($)	Mar. 01, 2021 USD ($)	Dec. 31, 2020 USD ($)	Mar. 30, 2020 MWh
Public Utilities, Commitments And Contingencies [Line Items]
Requested increase in annual distribution revenue			$ 14,000,000
Increase in revenue base rate			$ 104,500,000
Collection of increase in annual distribution revenues		$ 13,500,000
Energy efficiency cost recovery, requested change amount							$ 7,200,000	$ 5,900,000
Energy efficiency cost recovery, requested bonus							$ 2,300,000	$ 1,000,000
Rider charge from electricity relief program (per MWh) | MWh										0.33
Subsequent event
Public Utilities, Commitments And Contingencies [Line Items]
Requested increase in annual distribution revenue	$ 9,700,000
Increase in revenue base rate	$ 100,700,000
PUCT
Public Utilities, Commitments And Contingencies [Line Items]
Public utilities, costs of deployment				$ 9,000,000.0
COVID-19
Public Utilities, Commitments And Contingencies [Line Items]
Regulatory liability					$ 200,000	$ 0			$ 100,000