Fair Value Measurements (Reconciliation of Assets and Liabilities Measured at Fair Value on a Recurring Basis Using Unobservable Inputs) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Derivatives (net)
Balance at beginning of period	$ (77)	$ (102)
Total pretax realized or unrealized losses included in comprehensive income	(75)	(84)
Purchases	21	14
Settlements	(5)	(19)
Net transfers Out of Level 3		117
Total gains (losses) included on the Consolidated Balance Sheet	15	(3)
Ending balance	(121)	(77)
Duke Energy Indiana
Derivatives (net)
Balance at beginning of period	6	11
Purchases	18	10
Settlements	(16)	(13)
Total gains (losses) included on the Consolidated Balance Sheet	14	(2)
Ending balance	$ 22	6
Piedmont
Derivatives (net)
Balance at beginning of period		(117)
Net transfers Out of Level 3		$ 117