Investments in Debt and Equity Securities (Realized Gains and Losses) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
FV-NI:
Realized gains	$ 13	$ 60	$ 338	$ 161
Realized losses	16	43	148	136
AFS:
Realized gains	26	53	73	110
Realized losses	19	36	38	83
Duke Energy Carolinas
FV-NI:
Realized gains	10	34	46	101
Realized losses	12	26	82	95
AFS:
Realized gains	20	21	50	46
Realized losses	17	13	30	34
Progress Energy
FV-NI:
Realized gains	3	26	292	60
Realized losses	4	17	66	41
AFS:
Realized gains	6	31	17	62
Realized losses	2	23	7	49
Duke Energy Progress
FV-NI:
Realized gains	3	10	43	27
Realized losses	4	9	51	24
AFS:
Realized gains	6	2	17	4
Realized losses	$ 2		7	2
Duke Energy Florida
FV-NI:
Realized gains		16	249	33
Realized losses		8	$ 15	17
AFS:
Realized gains		29		58
Realized losses		$ 23		$ 47