Investments in Debt and Equity Securities (Maturities) (Details) $ in Millions	Dec. 31, 2017 USD ($)
Debt Instrument [Line Items]
Due in one year or less	$ 117
Due after one through five years	552
Due after five through ten years	554
Due after ten years	1,061
Total	2,284
Duke Energy Carolinas [Member]
Debt Instrument [Line Items]
Due in one year or less	9
Due after one through five years	204
Due after five through ten years	300
Due after ten years	521
Total	1,034
Progress Energy [Member]
Debt Instrument [Line Items]
Due in one year or less	94
Due after one through five years	301
Due after five through ten years	203
Due after ten years	474
Total	1,072
Duke Energy Progress [Member]
Debt Instrument [Line Items]
Due in one year or less	21
Due after one through five years	219
Due after five through ten years	146
Due after ten years	360
Total	746
Duke Energy Florida [Member]
Debt Instrument [Line Items]
Due in one year or less	73
Due after one through five years	82
Due after five through ten years	57
Due after ten years	114
Total	326
Duke Energy Indiana [Member]
Debt Instrument [Line Items]
Due in one year or less	5
Due after one through five years	12
Due after five through ten years	7
Due after ten years	7
Total	$ 31