Investments in Debt and Equity Securities (Maturities) (Details) $ in Millions	Dec. 31, 2015 USD ($)
Debt Instrument [Line Items]
Due in one year or less	$ 120
Due after one through five years	775
Due after five through ten years	598
Due after ten years	828
Total	2,321
Duke Energy Carolinas [Member]
Debt Instrument [Line Items]
Due in one year or less	13
Due after one through five years	187
Due after five through ten years	275
Due after ten years	438
Total	913
Progress Energy [Member]
Debt Instrument [Line Items]
Due in one year or less	94
Due after one through five years	496
Due after five through ten years	254
Due after ten years	339
Total	1,183
Duke Energy Progress [Member]
Debt Instrument [Line Items]
Due in one year or less	15
Due after one through five years	285
Due after five through ten years	206
Due after ten years	244
Total	750
Duke Energy Florida [Member]
Debt Instrument [Line Items]
Due in one year or less	79
Due after one through five years	211
Due after five through ten years	48
Due after ten years	95
Total	433
Duke Energy Indiana [Member]
Debt Instrument [Line Items]
Due in one year or less	2
Due after one through five years	14
Due after five through ten years	9
Due after ten years	3
Total	$ 28