Investments in Debt and Equity Securities (Maturities) (Details) $ in Millions	Jun. 30, 2018 USD ($)
Debt Instrument [Line Items]
Due in one year or less	$ 89
Due after one through five years	518
Due after five through 10 years	543
Due after 10 years	1,122
Total	2,272
Duke Energy Carolinas [Member]
Debt Instrument [Line Items]
Due in one year or less	12
Due after one through five years	163
Due after five through 10 years	286
Due after 10 years	556
Total	1,017
Progress Energy [Member]
Debt Instrument [Line Items]
Due in one year or less	69
Due after one through five years	286
Due after five through 10 years	207
Due after 10 years	488
Total	1,050
Duke Energy Progress [Member]
Debt Instrument [Line Items]
Due in one year or less	24
Due after one through five years	214
Due after five through 10 years	150
Due after 10 years	374
Total	762
Duke Energy Florida [Member]
Debt Instrument [Line Items]
Due in one year or less	45
Due after one through five years	72
Due after five through 10 years	57
Due after 10 years	114
Total	288
Duke Energy Indiana [Member]
Debt Instrument [Line Items]
Due in one year or less	3
Due after one through five years	20
Due after five through 10 years	4
Due after 10 years	14
Total	$ 41