Investments in Debt and Equity Securities (Maturities) (Details) $ in Millions	Dec. 31, 2020 USD ($)
Debt Securities, Available-for-sale [Line Items]
Due in one year or less	$ 149
Due after one through five years	922
Due after five through 10 years	671
Due after 10 years	1,260
Total	3,002
Duke Energy Carolinas
Debt Securities, Available-for-sale [Line Items]
Due in one year or less	14
Due after one through five years	299
Due after five through 10 years	279
Due after 10 years	658
Total	1,250
Progress Energy
Debt Securities, Available-for-sale [Line Items]
Due in one year or less	109
Due after one through five years	567
Due after five through 10 years	298
Due after 10 years	519
Total	1,493
Duke Energy Progress
Debt Securities, Available-for-sale [Line Items]
Due in one year or less	21
Due after one through five years	259
Due after five through 10 years	210
Due after 10 years	503
Total	993
Duke Energy Florida
Debt Securities, Available-for-sale [Line Items]
Due in one year or less	88
Due after one through five years	308
Due after five through 10 years	88
Due after 10 years	16
Total	500
Duke Energy Indiana
Debt Securities, Available-for-sale [Line Items]
Due in one year or less	3
Due after one through five years	17
Due after five through 10 years	10
Due after 10 years	15
Total	$ 45