Investments In Debt And Equity Securities (Maturities) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012
1 year	$ 325
1 through 5 years	428
6 to 10 years	363
Thereafter	776
Duke Energy Carolinas [Member]
1 year	44
1 through 5 years	152
6 to 10 years	191
Thereafter	371
Duke Energy Indiana [Member]
1 year	0
1 through 5 years	22
6 to 10 years	4
Thereafter	$ 2