Utility Plant and Nonutility Property (Narrative) (Details) - USD ($) $ in Millions		1 Months Ended	9 Months Ended
	Aug. 31, 2019	May 31, 2019	Sep. 30, 2020
Summer
Utility Plant And Non Utility Property [Line Items]
Percentage of direct expenses			66.70%
Percentage of ownership interest		66.70%
NND Project | Summer
Utility Plant And Non Utility Property [Line Items]
Percentage of ownership interest		55.00%
Santee Cooper | NND Project | Summer
Utility Plant And Non Utility Property [Line Items]
Percentage of ownership interest		11.70%
Ownership interest purchased		$ 8
Warranty Service Contract Assets
Utility Plant And Non Utility Property [Line Items]
Total consideration from sale of assets		$ 7
Contractual term of agreement to use brand			10 years
Warranty Service Contract Assets | Other Income (Expense), Net
Utility Plant And Non Utility Property [Line Items]
Gain on sale of assets	$ 7
Gain on sale of assets, after tax	$ 5