Regulatory and Rate Matters - TNMP Narrative (Details) - TNMP					9 Months Ended
	Jul. 18, 2022 USD ($)	Apr. 05, 2022 USD ($)	Jul. 01, 2021 USD ($)	Apr. 05, 2021 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2022 USD ($)	Sep. 24, 2022 USD ($)	May 27, 2022 USD ($)	Dec. 31, 2021 USD ($)	May 27, 2021 USD ($)	Dec. 31, 2020 USD ($)	Mar. 30, 2020 MWh
Public Utilities, Commitments And Contingencies [Line Items]
Requested increase in annual distribution revenue	$ 6,800,000	$ 9,700,000		$ 14,000,000
Increase in revenue base rate		$ 100,700,000		$ 104,500,000
Collection of increase in annual distribution revenues			$ 13,500,000
Energy efficiency cost recovery, requested change amount								$ 1,900,000		$ 7,200,000
Energy efficiency cost recovery, requested bonus								7,400,000		$ 2,300,000
Energy efficiency cost recovery factor, approved settlement amount							$ 7,300,000
Energy efficiency cost recovery factor, approved performance bonus								$ 1,900,000
Rider charge from electricity relief program (per MWh) | MWh												0.33
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						$ 700,000			$ 0		$ 100,000