Short-Term Debt - Additional Information (Detail) - USD ($)							12 Months Ended
	Jan. 29, 2021	Dec. 18, 2020	Feb. 06, 2020	Dec. 19, 2019	Mar. 23, 2018	Mar. 22, 2017	Dec. 31, 2020	Dec. 31, 2019
Line Of Credit Facility [Line Items]
Weighted-average interest rate							0.89%	2.56%
Line of credit facility maximum borrowing capacity		$ 80,000,000		$ 400,000,000			$ 1,250,000,000	$ 550,000,000
Line of credit facility, increase amount				$ 75,000,000
Lenders commitment amount		800,000,000
Increase of credit facility		$ 100,000,000
Amended And Restated Credit Agreement [Member]
Line Of Credit Facility [Line Items]
Line of credit facility maximum borrowing capacity						$ 325,000,000
364-day Credit Agreement [Member]
Line Of Credit Facility [Line Items]
Credit facility maturity period			364 days
Line of credit facility maximum borrowing capacity			$ 300,000,000
Credit facility maturity date			Feb. 04, 2021
364-day Credit Agreement [Member] | Subsequent Event [Member]
Line Of Credit Facility [Line Items]
Credit Facility extended maturity date	Apr. 29, 2021
3-year Accounts Receivable Facility [Member]
Line Of Credit Facility [Line Items]
Line of credit facility maximum borrowing capacity					$ 150,000,000		$ 150,000,000	$ 150,000,000
Credit facility maturity date					Mar. 22, 2021		Mar. 22, 2021	Mar. 22, 2021
Credit facility amendment date					Mar. 23, 2018
Loan agreement program and liquidity fees							0.70%
Interest rate description							TEC will pay program and liquidity fees, which total 70 basis points at December 31, 2020. Interest rates on the borrowings are based on prevailing asset-backed commercial paper rates, unless such rates are not available from conduit lenders, in which case the rates will be at an interest rate equal to either The Bank of Tokyo-Mitsubishi UFJ, Ltd.’s prime rate, the federal funds rate, or the London interbank deposit rate, plus a margin
Minimum [Member]
Line Of Credit Facility [Line Items]
Commitment fees, percentage							0.125%
Minimum [Member] | Amended And Restated Credit Agreement [Member]
Line Of Credit Facility [Line Items]
Debt instrument maturity date		Mar. 22, 2022				Dec. 17, 2018
Maximum [Member]
Line Of Credit Facility [Line Items]
Commitment fees, percentage							0.35%
Maximum [Member] | Amended And Restated Credit Agreement [Member]
Line Of Credit Facility [Line Items]
Debt instrument maturity date		Mar. 22, 2023				Mar. 22, 2022