Investments in Debt and Equity Securities (Maturities) (Details) $ in Millions	Jun. 30, 2015 USD ($)
Debt Instrument [Line Items]
Due in one year or less	$ 86
Due after one through five years	642
Due after five through 10 years	500
Due after 10 years	824
Total	2,052
Duke Energy Carolinas [Member]
Debt Instrument [Line Items]
Due in one year or less	10
Due after one through five years	197
Due after five through 10 years	275
Due after 10 years	445
Total	927
Progress Energy [Member]
Debt Instrument [Line Items]
Due in one year or less	55
Due after one through five years	345
Due after five through 10 years	156
Due after 10 years	322
Total	878
Duke Energy Progress [Member]
Debt Instrument [Line Items]
Due in one year or less	12
Due after one through five years	142
Due after five through 10 years	106
Due after 10 years	233
Total	493
Duke Energy Florida [Member]
Debt Instrument [Line Items]
Due in one year or less	43
Due after one through five years	203
Due after five through 10 years	50
Due after 10 years	89
Total	385
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	4
Total	$ 30