Investments in Debt and Equity Securities (Maturities) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014
Debt Instrument [Line Items]
Due in one year or less	$ 178
Due after one through five years	571
Due after five through ten years	464
Due after ten years	791
Total	2,004
Duke Energy Carolinas [Member]
Debt Instrument [Line Items]
Due in one year or less	1
Due after one through five years	155
Due after five through ten years	257
Due after ten years	409
Total	822
Progress Energy [Member]
Debt Instrument [Line Items]
Due in one year or less	161
Due after one through five years	350
Due after five through ten years	157
Due after ten years	319
Total	987
Duke Energy Progress [Member]
Debt Instrument [Line Items]
Due in one year or less	14
Due after one through five years	140
Due after five through ten years	109
Due after ten years	227
Total	490
Duke Energy Florida [Member]
Debt Instrument [Line Items]
Due in one year or less	147
Due after one through five years	210
Due after five through ten years	48
Due after ten years	92
Total	497
Duke Energy Indiana [Member]
Debt Instrument [Line Items]
Due in one year or less	1
Due after one through five years	17
Due after five through ten years	8
Due after ten years	4
Total	$ 30