Significant Accounting Policies - Additional Information (Detail) $ in Millions			12 Months Ended
	Aug. 06, 2019 USD ($)	Jul. 31, 2019	Dec. 31, 2019 USD ($) Segment	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Number of operating segments | Segment			2
Percentage of original cost of depreciable property			3.40%	3.50%	3.70%
Depreciation expense			$ 359	$ 345	$ 332
Suspension of depreciation expense granted	$ 15
Allowance for funds used during construction rate		5.97%	6.46%	6.46%	6.46%
Allowance for funds used during construction			$ 16	$ 15	$ 2
Investment tax credits			164	74
Receivables from contracts with customers			205	226
Unbilled revenues			61	67
Franchise fees and gross receipts taxes			$ 117	$ 120	$ 113
Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Discount rates used in estimating other self-insurance liabilities			2.66%	4.00%
Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Discount rates used in estimating other self-insurance liabilities			4.00%	4.01%
PGS [Member]
Summary Of Significant Accounting Policies [Line Items]
Reduction in annual depreciation expense			$ 10
Unbilled revenues			13
Tampa Electric [Member]
Summary Of Significant Accounting Policies [Line Items]
Unbilled revenues			$ 48