Investments in Debt and Equity Securities (Maturities) (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013
Debt Instrument [Line Items]
1 year	$ 340
1 through 5 years	392
6 to 10 years	366
Thereafter	772
Total	1,870
Duke Energy Carolinas [Member]
Debt Instrument [Line Items]
1 year	14
1 through 5 years	172
6 to 10 years	183
Thereafter	369
Total	738
Progress Energy [Member]
Debt Instrument [Line Items]
1 year	20
1 through 5 years	150
6 to 10 years	139
Thereafter	310
Total	619
Duke Energy Progress [Member]
Debt Instrument [Line Items]
1 year	12
1 through 5 years	132
6 to 10 years	76
Thereafter	201
Total	421
Duke Energy Florida [Member]
Debt Instrument [Line Items]
1 year	8
1 through 5 years	18
6 to 10 years	63
Thereafter	109
Total	198
Duke Energy Indiana [Member]
Debt Instrument [Line Items]
1 year	1
1 through 5 years	20
6 to 10 years	4
Thereafter	3
Total	$ 28