Investments in Debt and Equity Securities (Maturities) (Details) $ in Millions	Jun. 30, 2020 USD ($)
Debt Securities, Available-for-sale [Line Items]
Due in one year or less	$ 63
Due after one through five years	563
Due after five through 10 years	587
Due after 10 years	1,319
Total	2,532
Duke Energy Carolinas
Debt Securities, Available-for-sale [Line Items]
Due in one year or less	19
Due after one through five years	254
Due after five through 10 years	270
Due after 10 years	696
Total	1,239
Progress Energy
Debt Securities, Available-for-sale [Line Items]
Due in one year or less	30
Due after one through five years	244
Due after five through 10 years	226
Due after 10 years	543
Total	1,043
Duke Energy Progress
Debt Securities, Available-for-sale [Line Items]
Due in one year or less	28
Due after one through five years	235
Due after five through 10 years	219
Due after 10 years	509
Total	991
Duke Energy Florida
Debt Securities, Available-for-sale [Line Items]
Due in one year or less	2
Due after one through five years	9
Due after five through 10 years	7
Due after 10 years	34
Total	52
Duke Energy Indiana
Debt Securities, Available-for-sale [Line Items]
Due in one year or less	3
Due after one through five years	15
Due after five through 10 years	9
Due after 10 years	18
Total	$ 45