Investments in Debt and Equity Securities (Maturities) (Details) $ in Millions	Dec. 31, 2016 USD ($)
Debt Instrument [Line Items]
Due in one year or less	$ 94
Due after one through five years	653
Due after five through ten years	515
Due after ten years	946
Total	2,208
Duke Energy Carolinas [Member]
Debt Instrument [Line Items]
Due in one year or less	3
Due after one through five years	230
Due after five through ten years	260
Due after ten years	505
Total	998
Progress Energy [Member]
Debt Instrument [Line Items]
Due in one year or less	84
Due after one through five years	347
Due after five through ten years	187
Due after ten years	398
Total	1,016
Duke Energy Progress [Member]
Debt Instrument [Line Items]
Due in one year or less	28
Due after one through five years	190
Due after five through ten years	142
Due after ten years	303
Total	663
Duke Energy Florida [Member]
Debt Instrument [Line Items]
Due in one year or less	56
Due after one through five years	157
Due after five through ten years	45
Due after ten years	95
Total	353
Duke Energy Indiana [Member]
Debt Instrument [Line Items]
Due in one year or less	3
Due after one through five years	13
Due after five through ten years	9
Due after ten years	6
Total	$ 31