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, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Derivatives (net)
Balance at beginning of period	$ (126)	$ (88)	$ (77)	$ (102)
Total pretax realized or unrealized losses included in comprehensive income	(31)		(75)
Purchases, sales, issuances and settlements:
Purchases	21	14	21	14
Settlements	(1)	(6)	(8)	(15)
Total gains (losses) included on the Condensed Consolidated Balance Sheet	6	(12)	8	11
Balance at end of period	(131)	(92)	(131)	(92)
Duke Energy Indiana
Derivatives (net)
Balance at beginning of period	2	2	6	11
Purchases, sales, issuances and settlements:
Purchases	18	10	18	10
Settlements	(3)	(4)	(9)	(10)
Total gains (losses) included on the Condensed Consolidated Balance Sheet	5	2	7	(1)
Balance at end of period	$ 22	10	$ 22	10
Piedmont
Derivatives (net)
Balance at beginning of period		(91)		(117)
Purchases, sales, issuances and settlements:
Total (losses) gains and settlements		(14)		12
Balance at end of period		$ (105)		$ (105)