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, 2021	Mar. 31, 2020
Derivatives (net)
Balance at beginning of period	$ (77)	$ (102)
Total pretax realized or unrealized losses included in comprehensive income	(44)
Purchases, sales, issuances and settlements:
Settlements	(7)	(9)
Total gains included on the Condensed Consolidated Balance Sheet	2	23
Balance at end of period	(126)	(88)
Duke Energy Indiana
Derivatives (net)
Balance at beginning of period	6	11
Purchases, sales, issuances and settlements:
Settlements	(6)	(6)
Total gains included on the Condensed Consolidated Balance Sheet	2	(3)
Balance at end of period	$ 2	2
Piedmont
Derivatives (net)
Balance at beginning of period		(117)
Purchases, sales, issuances and settlements:
Total gains and settlements		26
Balance at end of period		$ (91)