Investments in Debt and Equity Securities (Maturities) (Details) $ in Millions	Jun. 30, 2017 USD ($)
Debt Instrument [Line Items]
Due in one year or less	$ 86
Due after one through five years	631
Due after five through 10 years	503
Due after 10 years	1,064
Total	2,284
Duke Energy Carolinas [Member]
Debt Instrument [Line Items]
Due in one year or less	4
Due after one through five years	224
Due after five through 10 years	245
Due after 10 years	543
Total	1,016
Progress Energy [Member]
Debt Instrument [Line Items]
Due in one year or less	72
Due after one through five years	347
Due after five through 10 years	196
Due after 10 years	470
Total	1,085
Duke Energy Progress [Member]
Debt Instrument [Line Items]
Due in one year or less	18
Due after one through five years	220
Due after five through 10 years	144
Due after 10 years	359
Total	741
Duke Energy Florida [Member]
Debt Instrument [Line Items]
Due in one year or less	54
Due after one through five years	127
Due after five through 10 years	52
Due after 10 years	111
Total	344
Duke Energy Indiana [Member]
Debt Instrument [Line Items]
Due in one year or less	3
Due after one through five years	14
Due after five through 10 years	8
Due after 10 years	6
Total	$ 31