Investments in Debt and Equity Securities (Realized Gains and Losses) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
FV-NI:
Realized gains	$ 366	$ 172	$ 168
Realized losses	174	151	126
AFS:
Realized gains	96	94	22
Realized losses	51	67	51
Duke Energy Carolinas
FV-NI:
Realized gains	64	113	89
Realized losses	99	107	73
AFS:
Realized gains	60	55	19
Realized losses	37	38	35
Progress Energy
FV-NI:
Realized gains	302	59	79
Realized losses	75	44	53
AFS:
Realized gains	24	36	3
Realized losses	13	29	15
Duke Energy Progress
FV-NI:
Realized gains	52	38	68
Realized losses	59	33	48
AFS:
Realized gains	24	7	2
Realized losses	13	5	10
Duke Energy Florida
FV-NI:
Realized gains	250	21	11
Realized losses	16	11	5
AFS:
Realized gains	0	29	1
Realized losses	$ 0	$ 24	$ 5