Investments in Debt and Equity Securities (Maturities) (Details) $ in Millions	Mar. 31, 2017 USD ($)
Debt Instrument [Line Items]
Due in one year or less	$ 82
Due after one through five years	640
Due after five through 10 years	514
Due after 10 years	986
Total	2,222
Duke Energy Carolinas [Member]
Debt Instrument [Line Items]
Due in one year or less	2
Due after one through five years	221
Due after five through 10 years	269
Due after 10 years	517
Total	1,009
Progress Energy [Member]
Debt Instrument [Line Items]
Due in one year or less	72
Due after one through five years	355
Due after five through 10 years	189
Due after 10 years	417
Total	1,033
Duke Energy Progress [Member]
Debt Instrument [Line Items]
Due in one year or less	17
Due after one through five years	215
Due after five through 10 years	142
Due after 10 years	316
Total	690
Duke Energy Florida [Member]
Debt Instrument [Line Items]
Due in one year or less	55
Due after one through five years	140
Due after five through 10 years	47
Due after 10 years	101
Total	343
Duke Energy Indiana [Member]
Debt Instrument [Line Items]
Due in one year or less	2
Due after one through five years	15
Due after five through 10 years	9
Due after 10 years	5
Total	$ 31