Investments in Debt and Equity Securities (Maturities) (Details) $ in Millions	Sep. 30, 2015 USD ($)
Debt Instrument [Line Items]
Due in one year or less	$ 74
Due after one through five years	781
Due after five through 10 years	635
Due after 10 years	812
Total	2,302
Duke Energy Carolinas [Member]
Debt Instrument [Line Items]
Due in one year or less	13
Due after one through five years	209
Due after five through 10 years	293
Due after 10 years	423
Total	938
Progress Energy [Member]
Debt Instrument [Line Items]
Due in one year or less	38
Due after one through five years	476
Due after five through 10 years	271
Due after 10 years	333
Total	1,118
Duke Energy Progress [Member]
Debt Instrument [Line Items]
Due in one year or less	12
Due after one through five years	278
Due after five through 10 years	219
Due after 10 years	240
Total	749
Duke Energy Florida [Member]
Debt Instrument [Line Items]
Due in one year or less	26
Due after one through five years	198
Due after five through 10 years	52
Due after 10 years	93
Total	369
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