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		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Derivatives (net)
Balance at beginning of period	$ (131)	$ (92)	$ (77)	$ (102)
Total pretax realized or unrealized losses included in comprehensive income	(11)	(102)	(86)	(102)
Purchases, sales, issuances and settlements:
Purchases			21	14
Settlements	4	(3)	(4)	(18)
Total gains (losses) included on the Condensed Consolidated Balance Sheet	7	(6)	15	5
Balance at end of period	(131)	(203)	(131)	(203)
Duke Energy Indiana
Derivatives (net)
Balance at beginning of period	22	10	6	11
Purchases, sales, issuances and settlements:
Purchases			18	10
Settlements	(3)	(3)	(12)	(13)
Total gains (losses) included on the Condensed Consolidated Balance Sheet	5	1	12
Balance at end of period	$ 24	8	$ 24	8
Piedmont
Derivatives (net)
Balance at beginning of period		(105)		(117)
Purchases, sales, issuances and settlements:
Total (losses) gains and settlements		(6)		6
Balance at end of period		$ (111)		$ (111)