Summary of Significant Accounting Policies - Summary of Property, Plant and Equipment by Classification (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($) mi	Dec. 31, 2019 USD ($) mi	Dec. 31, 2018 USD ($)
Property, Plant and Equipment [Line Items]
Contributions in Aid of Construction	$ 2,900	$ 2,100
Public Utilities, Allowance for Funds Used During Construction, Description	$ 700	700	$ 1,900
Number of Months to Establish ROU Asset and Liability	12 months
Property, plant and equipment
Total property, plant and equipment	$ 1,908,992	1,746,532
Less: Accumulated depreciation and amortization	(368,743)	(336,876)
Net property, plant and equipment	1,601,178	1,463,797
Construction Work in Progress	60,929	54,141
Jointly Owned Pipeline [Member]
Property, plant and equipment
Accumulated Depreciation, Depletion and Amortization, Sale or Disposal of Property, Plant and Equipment	300
Natural Gas
Property, plant and equipment
Accumulated Depreciation, Depletion and Amortization, Sale or Disposal of Property, Plant and Equipment	1,700	1,500
Natural Gas Distribution [Member] | Delmarva and Florida [Member]
Property, plant and equipment
Total property, plant and equipment	782,329	705,095
Natural Gas Transmission [Member] | Delmarva Peninsula, Pennsylvania and Florida [Member]
Property, plant and equipment
Total property, plant and equipment	667,538	608,727
Natural Gas Transmission [Member] | OHIO
Property, plant and equipment
Total property, plant and equipment	87,962	73,658
Electric distribution | Florida
Property, plant and equipment
Total property, plant and equipment	127,710	127,651
Propane Operations [Member] | Mid-Atlantic and Florida [Member]
Property, plant and equipment
Total property, plant and equipment	151,258	141,945
Electricity and Steam Generation [Member] | Florida
Property, plant and equipment
Total property, plant and equipment	36,521	35,436
Mobile CNG Utility and Pipeline Solutions [Member] | Florida
Property, plant and equipment
Total property, plant and equipment	24,905	14,014
Other
Property, plant and equipment
Total property, plant and equipment	30,769	$ 40,006
Natural Gas Operations
Property, plant and equipment
Net property, plant and equipment	$ 6,700
Miles Of Natural Gas Pipeline | mi	26	16
Jointly Owned Pipeline [Member]
Property, plant and equipment
Net property, plant and equipment	$ 26,400