Fair Value Measurements (Reconciliation of Assets and Liabilities Measured At Fair Value On A Recurring Basis Using Unobservable Inputs) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Derivatives (net)
Balance at beginning of period	$ (102)	$ (113)
Purchases, sales, issuances and settlements:
Settlements	(9)	(12)
Total gains included on the Condensed Consolidated Balance Sheet	23	10
Balance at end of period	(88)	(115)
Duke Energy Indiana
Derivatives (net)
Balance at beginning of period	11	22
Purchases, sales, issuances and settlements:
Settlements	(6)	(10)
Total gains included on the Condensed Consolidated Balance Sheet	(3)	(7)
Balance at end of period	2	5
Piedmont Natural Gas
Derivatives (net)
Balance at beginning of period	(117)	(141)
Purchases, sales, issuances and settlements:
Total gains and settlements	26	20
Balance at end of period	$ (91)	$ (121)