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, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Derivatives (net)
Balance at beginning of period	$ (92)	$ (79)	$ (102)	$ (113)
Total pretax realized or unrealized gains included in comprehensive income	(102)		(102)
Purchases, sales, issuances and settlements:
Purchases			14	38
Settlements	(3)	(9)	(18)	(32)
Total (losses) gains included on the Condensed Consolidated Balance Sheet	(6)	(2)	5	17
Balance at end of period	(203)	(90)	(203)	(90)
Duke Energy Indiana
Derivatives (net)
Balance at beginning of period	10	28	11	22
Purchases, sales, issuances and settlements:
Purchases			10	29
Settlements	(3)	(7)	(13)	(26)
Total (losses) gains included on the Condensed Consolidated Balance Sheet	1	(5)	0	(9)
Balance at end of period	8	16	8	16
Piedmont Natural Gas
Derivatives (net)
Balance at beginning of period	(105)	(114)	(117)	(141)
Purchases, sales, issuances and settlements:
Total (losses) gains and settlements	(6)	3	6	30
Balance at end of period	$ (111)	$ (111)	$ (111)	$ (111)