Investments in Debt and Equity Securities (Maturities) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013
Debt Instrument [Line Items]
1 year	$ 185
1 through 5 years	394
6 to 10 years	434
Thereafter	790
Total	1,803
Duke Energy Carolinas [Member]
Debt Instrument [Line Items]
1 year	23
1 through 5 years	175
6 to 10 years	223
Thereafter	410
Total	831
Progress Energy [Member]
Debt Instrument [Line Items]
1 year	14
1 through 5 years	162
6 to 10 years	150
Thereafter	294
Total	620
Duke Energy Progress [Member]
Debt Instrument [Line Items]
1 year	6
1 through 5 years	125
6 to 10 years	88
Thereafter	201
Total	420
Duke Energy Florida [Member]
Debt Instrument [Line Items]
1 year	8
1 through 5 years	37
6 to 10 years	62
Thereafter	94
Total	201
Duke Energy Indiana [Member]
Debt Instrument [Line Items]
1 year	2
1 through 5 years	21
6 to 10 years	4
Thereafter	1
Total	$ 28