Investments in Debt and Equity Securities (Maturities) (Details) $ in Millions	Sep. 30, 2021 USD ($)
Debt Securities, Available-for-sale [Line Items]
Due in one year or less	$ 151
Due after one through five years	954
Due after five through 10 years	639
Due after 10 years	1,482
Total	3,226
Duke Energy Carolinas
Debt Securities, Available-for-sale [Line Items]
Due in one year or less	3
Due after one through five years	343
Due after five through 10 years	268
Due after 10 years	847
Total	1,461
Progress Energy
Debt Securities, Available-for-sale [Line Items]
Due in one year or less	121
Due after one through five years	548
Due after five through 10 years	286
Due after 10 years	553
Total	1,508
Duke Energy Progress
Debt Securities, Available-for-sale [Line Items]
Due in one year or less	22
Due after one through five years	244
Due after five through 10 years	247
Due after 10 years	517
Total	1,030
Duke Energy Florida
Debt Securities, Available-for-sale [Line Items]
Due in one year or less	99
Due after one through five years	304
Due after five through 10 years	39
Due after 10 years	36
Total	478
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	8
Due after 10 years	15
Total	$ 46