Investments in Debt and Equity Securities (Maturities) (Details) $ in Millions	Sep. 30, 2020 USD ($)
Debt Securities, Available-for-sale [Line Items]
Due in one year or less	$ 53
Due after one through five years	558
Due after five through 10 years	608
Due after 10 years	1,313
Total	2,532
Duke Energy Carolinas
Debt Securities, Available-for-sale [Line Items]
Due in one year or less	13
Due after one through five years	247
Due after five through 10 years	278
Due after 10 years	694
Total	1,232
Progress Energy
Debt Securities, Available-for-sale [Line Items]
Due in one year or less	15
Due after one through five years	256
Due after five through 10 years	232
Due after 10 years	542
Total	1,045
Duke Energy Progress
Debt Securities, Available-for-sale [Line Items]
Due in one year or less	14
Due after one through five years	246
Due after five through 10 years	224
Due after 10 years	508
Total	992
Duke Energy Florida
Debt Securities, Available-for-sale [Line Items]
Due in one year or less	1
Due after one through five years	10
Due after five through 10 years	8
Due after 10 years	34
Total	53
Duke Energy Indiana
Debt Securities, Available-for-sale [Line Items]
Due in one year or less	4
Due after one through five years	16
Due after five through 10 years	9
Due after 10 years	16
Total	$ 45