Investments in Debt and Equity Securities (Maturities) (Details) $ in Millions	Jun. 30, 2021 USD ($)
Debt Securities, Available-for-sale [Line Items]
Due in one year or less	$ 162
Due after one through five years	1,022
Due after five through 10 years	683
Due after 10 years	1,429
Total	3,296
Duke Energy Carolinas
Debt Securities, Available-for-sale [Line Items]
Due in one year or less	10
Due after one through five years	385
Due after five through 10 years	301
Due after 10 years	772
Total	1,468
Progress Energy
Debt Securities, Available-for-sale [Line Items]
Due in one year or less	112
Due after one through five years	578
Due after five through 10 years	302
Due after 10 years	579
Total	1,571
Duke Energy Progress
Debt Securities, Available-for-sale [Line Items]
Due in one year or less	16
Due after one through five years	262
Due after five through 10 years	243
Due after 10 years	540
Total	1,061
Duke Energy Florida
Debt Securities, Available-for-sale [Line Items]
Due in one year or less	96
Due after one through five years	316
Due after five through 10 years	59
Due after 10 years	39
Total	510
Duke Energy Indiana
Debt Securities, Available-for-sale [Line Items]
Due in one year or less	4
Due after one through five years	18
Due after five through 10 years	8
Due after 10 years	15
Total	$ 45