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		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Derivatives (net)
Balance at beginning of period	$ (88)	$ (115)	$ (102)	$ (113)
Purchases, sales, issuances and settlements:
Purchases	14	38	14	38
Settlements	(6)	(11)	(15)	(23)
Total (losses) gains included on the Condensed Consolidated Balance Sheet	(12)	9	11	19
Balance at end of period	(92)	(79)	(92)	(79)
Duke Energy Indiana
Derivatives (net)
Balance at beginning of period	2	5	11	22
Purchases, sales, issuances and settlements:
Purchases	10	29	10	29
Settlements	(4)	(9)	(10)	(19)
Total (losses) gains included on the Condensed Consolidated Balance Sheet	2	3	(1)	(4)
Balance at end of period	10	28	10	28
Piedmont Natural Gas
Derivatives (net)
Balance at beginning of period	(91)	(121)	(117)	(141)
Purchases, sales, issuances and settlements:
Total gains and settlements	(14)	7	12	27
Balance at end of period	$ (105)	$ (114)	$ (105)	$ (114)