Investments in Debt and Equity Securities (Maturities) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014
Debt Instrument [Line Items]
1 year	$ 59
1 through 5 years	433
6 to 10 years	499
Thereafter	774
Total	1,765
Duke Energy Carolinas [Member]
Debt Instrument [Line Items]
1 year	24
1 through 5 years	165
6 to 10 years	305
Thereafter	357
Total	851
Progress Energy [Member]
Debt Instrument [Line Items]
1 year	16
1 through 5 years	212
6 to 10 years	136
Thereafter	323
Total	687
Duke Energy Progress [Member]
Debt Instrument [Line Items]
1 year	5
1 through 5 years	136
6 to 10 years	89
Thereafter	218
Total	448
Duke Energy Florida [Member]
Debt Instrument [Line Items]
1 year	11
1 through 5 years	76
6 to 10 years	47
Thereafter	105
Total	239
Duke Energy Indiana [Member]
Debt Instrument [Line Items]
1 year	1
1 through 5 years	20
6 to 10 years	5
Thereafter	2
Total	$ 28