Investments In Debt And Equity Securities (Maturities) (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012
1 year	$ 164
1 through 5 years	345
6 to 10 years	212
Thereafter	471
Duke Energy Carolinas [Member]
1 year	45
1 through 5 years	146
6 to 10 years	174
Thereafter	369
Duke Energy Indiana [Member]
1 year	0
1 through 5 years	21
6 to 10 years	5
Thereafter	$ 2