Investments in Debt and Equity Securities (Maturities) (Details) $ in Millions	Jun. 30, 2016 USD ($)
Debt Instrument [Line Items]
Due in one year or less	$ 88
Due after one through five years	660
Due after five through 10 years	511
Due after 10 years	991
Total	2,250
Duke Energy Carolinas [Member]
Debt Instrument [Line Items]
Due in one year or less	6
Due after one through five years	198
Due after five through 10 years	235
Due after 10 years	533
Total	972
Progress Energy [Member]
Debt Instrument [Line Items]
Due in one year or less	65
Due after one through five years	375
Due after five through 10 years	200
Due after 10 years	407
Total	1,047
Duke Energy Progress [Member]
Debt Instrument [Line Items]
Due in one year or less	14
Due after one through five years	191
Due after five through 10 years	154
Due after 10 years	310
Total	669
Duke Energy Florida [Member]
Debt Instrument [Line Items]
Due in one year or less	51
Due after one through five years	184
Due after five through 10 years	46
Due after 10 years	97
Total	378
Duke Energy Indiana [Member]
Debt Instrument [Line Items]
Due in one year or less	2
Due after one through five years	16
Due after five through 10 years	8
Due after 10 years	5
Total	$ 31