Investments in Debt and Equity Securities (Maturities) (Details) $ in Millions	Sep. 30, 2019 USD ($)
Debt Securities, Available-for-sale [Line Items]
Due in one year or less	$ 400
Due after one through five years	524
Due after five through 10 years	450
Due after 10 years	1,259
Total	2,633
Duke Energy Carolinas [Member]
Debt Securities, Available-for-sale [Line Items]
Due in one year or less	65
Due after one through five years	220
Due after five through 10 years	187
Due after 10 years	687
Total	1,159
Progress Energy [Member]
Debt Securities, Available-for-sale [Line Items]
Due in one year or less	328
Due after one through five years	253
Due after five through 10 years	209
Due after 10 years	465
Total	1,255
Duke Energy Progress [Member]
Debt Securities, Available-for-sale [Line Items]
Due in one year or less	48
Due after one through five years	243
Due after five through 10 years	201
Due after 10 years	431
Total	923
Duke Energy Florida [Member]
Debt Securities, Available-for-sale [Line Items]
Due in one year or less	280
Due after one through five years	10
Due after five through 10 years	8
Due after 10 years	34
Total	332
Duke Energy Indiana [Member]
Debt Securities, Available-for-sale [Line Items]
Due in one year or less	4
Due after one through five years	15
Due after five through 10 years	5
Due after 10 years	19
Total	$ 43