Business Segments (Major Customer Disclosure) (Details) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2019 USD ($) segment	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Revenue, Major Customer [Line Items]
Revenues	$ 6,103	$ 6,940	$ 5,873	$ 6,163	$ 6,115	$ 6,628	$ 5,643	$ 6,135	$ 25,079	$ 24,521	$ 23,565
Duke Energy Progress
Revenue, Major Customer [Line Items]
Revenues	$ 1,398	$ 1,688	$ 1,387	$ 1,484	$ 1,366	$ 1,582	$ 1,291	$ 1,460	$ 5,957	$ 5,699	$ 5,129
Number of reportable segments | segment									1