Leases - Additional Information (Detail) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)
Operating Leased Assets [Line Items]
Operating lease, description		TEC has operating leases for buildings, land, telecommunication services and rail cars.
Operating lease, existence of option to extend		true
Operating lease options to extend		options to extend the leases for up to an additional 65 years
Operating lease expense	$ 1	$ 2
Option to purchase assets related to CNG stations		Customers have the option to purchase the assets related to the CNG stations at any time after 2021 by paying a make-whole payment at the date of the purchase based on a targeted internal rate of return
Maximum [Member]
Operating Leased Assets [Line Items]
Operating lease renewal term	67 years	67 years
Minimum [Member]
Operating Leased Assets [Line Items]
Operating lease renewal term	2 years	2 years