Investments in Debt and Equity Securities (Maturities) (Details) $ in Millions	Mar. 31, 2021 USD ($)
Debt Securities, Available-for-sale [Line Items]
Due in one year or less	$ 152
Due after one through five years	1,013
Due after five through 10 years	693
Due after 10 years	1,254
Total	3,112
Duke Energy Carolinas
Debt Securities, Available-for-sale [Line Items]
Due in one year or less	7
Due after one through five years	375
Due after five through 10 years	310
Due after 10 years	652
Total	1,344
Progress Energy
Debt Securities, Available-for-sale [Line Items]
Due in one year or less	116
Due after one through five years	579
Due after five through 10 years	289
Due after 10 years	533
Total	1,517
Duke Energy Progress
Debt Securities, Available-for-sale [Line Items]
Due in one year or less	18
Due after one through five years	267
Due after five through 10 years	217
Due after 10 years	501
Total	1,003
Duke Energy Florida
Debt Securities, Available-for-sale [Line Items]
Due in one year or less	98
Due after one through five years	312
Due after five through 10 years	72
Due after 10 years	32
Total	514
Duke Energy Indiana
Debt Securities, Available-for-sale [Line Items]
Due in one year or less	5
Due after one through five years	18
Due after five through 10 years	9
Due after 10 years	13
Total	$ 45