Investments in Debt and Equity Securities (Maturities) (Details) $ in Millions	Dec. 31, 2018 USD ($)
Debt Securities, Available-for-sale [Line Items]
Due in one year or less	$ 98
Due after one through five years	501
Due after five through ten years	570
Due after ten years	1,222
Total	2,391
Duke Energy Carolinas [Member]
Debt Securities, Available-for-sale [Line Items]
Due in one year or less	6
Due after one through five years	142
Due after five through ten years	303
Due after ten years	589
Total	1,040
Progress Energy [Member]
Debt Securities, Available-for-sale [Line Items]
Due in one year or less	87
Due after one through five years	306
Due after five through ten years	216
Due after ten years	541
Total	1,150
Duke Energy Progress [Member]
Debt Securities, Available-for-sale [Line Items]
Due in one year or less	49
Due after one through five years	231
Due after five through ten years	161
Due after ten years	419
Total	860
Duke Energy Florida [Member]
Debt Securities, Available-for-sale [Line Items]
Due in one year or less	38
Due after one through five years	75
Due after five through ten years	55
Due after ten years	122
Total	290
Duke Energy Indiana [Member]
Debt Securities, Available-for-sale [Line Items]
Due in one year or less	3
Due after one through five years	20
Due after five through ten years	4
Due after ten years	14
Total	$ 41