Investments in Debt and Equity Securities (Maturities) (Details) $ in Millions	Sep. 30, 2016 USD ($)
Debt Instrument [Line Items]
Due in one year or less	$ 92
Due after one through five years	655
Due after five through 10 years	529
Due after 10 years	1,015
Total	2,291
Duke Energy Carolinas [Member]
Debt Instrument [Line Items]
Due in one year or less	3
Due after one through five years	206
Due after five through 10 years	268
Due after 10 years	543
Total	1,020
Progress Energy [Member]
Debt Instrument [Line Items]
Due in one year or less	67
Due after one through five years	372
Due after five through 10 years	187
Due after 10 years	422
Total	1,048
Duke Energy Progress [Member]
Debt Instrument [Line Items]
Due in one year or less	21
Due after one through five years	200
Due after five through 10 years	142
Due after 10 years	320
Total	683
Duke Energy Florida [Member]
Debt Instrument [Line Items]
Due in one year or less	46
Due after one through five years	172
Due after five through 10 years	45
Due after 10 years	102
Total	365
Duke Energy Indiana [Member]
Debt Instrument [Line Items]
Due in one year or less	3
Due after one through five years	9
Due after five through 10 years	13
Due after 10 years	5
Total	$ 30