Investments in Debt and Equity Securities (Maturities) (Details) $ in Millions	Mar. 31, 2016 USD ($)
Debt Instrument [Line Items]
Due in one year or less	$ 136
Due after one through five years	769
Due after five through 10 years	559
Due after 10 years	915
Total	2,379
Duke Energy Carolinas [Member]
Debt Instrument [Line Items]
Due in one year or less	14
Due after one through five years	195
Due after five through 10 years	224
Due after 10 years	520
Total	953
Progress Energy [Member]
Debt Instrument [Line Items]
Due in one year or less	101
Due after one through five years	486
Due after five through 10 years	264
Due after 10 years	346
Total	1,197
Duke Energy Progress [Member]
Debt Instrument [Line Items]
Due in one year or less	37
Due after one through five years	282
Due after five through 10 years	219
Due after 10 years	250
Total	788
Duke Energy Florida [Member]
Debt Instrument [Line Items]
Due in one year or less	64
Due after one through five years	204
Due after five through 10 years	45
Due after 10 years	96
Total	409
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 10 years	9
Due after 10 years	4
Total	$ 29