Related Party Transactions - Schedule of Related Parties (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Related Party Transaction [Line Items]
Natural gas sales to/(from) affiliates	$ (38)	$ (4)	$ 0
Services received from affiliates	65	67	66
Dividends to TECO Energy	362	292
Equity contributions from TECO Energy	345	190
Accounts receivable	3	2
Accounts payable	20	19
Taxes receivable	1	3
Taxes payable	4	2
TECO Energy [Member]
Related Party Transaction [Line Items]
Dividends to TECO Energy	362	292	289
Equity contributions from TECO Energy	$ 345	$ 190	$ 150

Natural gas sales to (from) affiliates.

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