Investments in Debt and Equity Securities (Maturities) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014
Debt Instrument [Line Items]
Due in one year or less	$ 33
Due after one through five years	452
Due after five through 10 years	457
Due after 10 years	795
Total	1,737
Duke Energy Carolinas [Member]
Debt Instrument [Line Items]
Due in one year or less	2
Due after one through five years	171
Due after five through 10 years	256
Due after 10 years	380
Total	809
Progress Energy [Member]
Debt Instrument [Line Items]
Due in one year or less	21
Due after one through five years	218
Due after five through 10 years	145
Due after 10 years	328
Total	712
Duke Energy Progress [Member]
Debt Instrument [Line Items]
Due in one year or less	10
Due after one through five years	147
Due after five through 10 years	94
Due after 10 years	217
Total	468
Duke Energy Florida [Member]
Debt Instrument [Line Items]
Due in one year or less	11
Due after one through five years	71
Due after five through 10 years	51
Due after 10 years	111
Total	244
Duke Energy Indiana [Member]
Debt Instrument [Line Items]
Due in one year or less	1
Due after one through five years	18
Due after five through 10 years	8
Due after 10 years	3
Total	$ 30