Investments in Debt and Equity Securities (Maturities) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015
Debt Instrument [Line Items]
Due in one year or less	$ 110
Due after one through five years	603
Due after five through 10 years	488
Due after 10 years	804
Total	2,005
Duke Energy Carolinas [Member]
Debt Instrument [Line Items]
Due in one year or less	5
Due after one through five years	177
Due after five through 10 years	257
Due after 10 years	407
Total	846
Progress Energy [Member]
Debt Instrument [Line Items]
Due in one year or less	84
Due after one through five years	350
Due after five through 10 years	160
Due after 10 years	326
Total	920
Duke Energy Progress [Member]
Debt Instrument [Line Items]
Due in one year or less	12
Due after one through five years	147
Due after five through 10 years	113
Due after 10 years	233
Total	505
Duke Energy Florida [Member]
Debt Instrument [Line Items]
Due in one year or less	72
Due after one through five years	203
Due after five through 10 years	47
Due after 10 years	93
Total	415
Duke Energy Indiana [Member]
Debt Instrument [Line Items]
Due in one year or less	2
Due after one through five years	17
Due after five through 10 years	8
Due after 10 years	3
Total	$ 30