Investments in Debt and Equity Securities (Realized Gains and Losses) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
FV-NI:
Realized gains	$ 34	$ 13	$ 320	$ 338
Realized losses	40	16	100	148
AFS:
Realized gains	17	26	51	73
Realized losses	15	19	46	38
Duke Energy Carolinas
FV-NI:
Realized gains	25	10	243	46
Realized losses	29	12	68	82
AFS:
Realized gains	10	20	35	50
Realized losses	10	17	32	30
Progress Energy
FV-NI:
Realized gains	9	3	77	292
Realized losses	11	4	32	66
AFS:
Realized gains	7	6	14	17
Realized losses	6	2	12	7
Duke Energy Progress
FV-NI:
Realized gains	9	3	76	43
Realized losses	11	4	31	51
AFS:
Realized gains	6	6	13	17
Realized losses	5	$ 2	11	7
Duke Energy Florida
FV-NI:
Realized gains			1	249
Realized losses			1	$ 15
AFS:
Realized gains	1		1
Realized losses	$ 1		$ 1