Investments in Debt and Equity Securities (Realized Gains and Losses) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
FV-NI:
Realized gains	$ 146	$ 302	$ 286	$ 325
Realized losses	37	67	60	132
AFS:
Realized gains	16	27	34	47
Realized losses	18	13	31	19
Duke Energy Carolinas
FV-NI:
Realized gains	90	27	218	36
Realized losses	23	25	39	70
AFS:
Realized gains	12	18	25	30
Realized losses	13	8	22	13
Progress Energy
FV-NI:
Realized gains	56	275	68	289
Realized losses	14	42	21	62
AFS:
Realized gains	3	6	7	11
Realized losses	3	4	6	5
Duke Energy Progress
FV-NI:
Realized gains	55	26	67	40
Realized losses	13	27	20	47
AFS:
Realized gains	3	6	7	11
Realized losses	3	4	6	5
Duke Energy Florida
FV-NI:
Realized gains	1	249	1	249
Realized losses	$ 1	$ 15	$ 1	$ 15