Investments in Debt and Equity Securities (Maturities) (Details) $ in Millions	Mar. 31, 2020 USD ($)
Debt Securities, Available-for-sale [Line Items]
Due in one year or less	$ 333
Due after one through five years	538
Due after five through 10 years	465
Due after 10 years	1,375
Total	2,711
Duke Energy Carolinas
Debt Securities, Available-for-sale [Line Items]
Due in one year or less	25
Due after one through five years	234
Due after five through 10 years	188
Due after 10 years	734
Total	1,181
Progress Energy
Debt Securities, Available-for-sale [Line Items]
Due in one year or less	302
Due after one through five years	236
Due after five through 10 years	214
Due after 10 years	541
Total	1,293
Duke Energy Progress
Debt Securities, Available-for-sale [Line Items]
Due in one year or less	26
Due after one through five years	227
Due after five through 10 years	207
Due after 10 years	506
Total	966
Duke Energy Florida
Debt Securities, Available-for-sale [Line Items]
Due in one year or less	276
Due after one through five years	9
Due after five through 10 years	7
Due after 10 years	35
Total	327
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	7
Due after 10 years	16
Total	$ 43