Business Segments (Major Customer Disclosure) (Details) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2018 USD ($) segment	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Revenue, Major Customer [Line Items]
Revenues	$ 6,115	$ 6,628	$ 5,643	$ 6,135	$ 5,799	$ 6,482	$ 5,555	$ 5,729	$ 24,521	$ 23,565	$ 22,743
Duke Energy Progress [Member]
Revenue, Major Customer [Line Items]
Revenues	$ 1,366	$ 1,582	$ 1,291	$ 1,460	$ 1,251	$ 1,460	$ 1,199	$ 1,219	$ 5,699	$ 5,129	$ 5,277
Number of Reportable Segments | segment									1