Risk Management, Derivative Instruments And Hedging Activities (Underlying Notional Amounts For Derivative Instruments Accounted For At Fair Value) (Details)	9 Months Ended	12 Months Ended
	Sep. 30, 2012 MWh dth gal mwm	Dec. 31, 2011 dth MWh T
Electricity-energy (Gigawatt-hours)	27,820,000,000	14,118,000,000
Emission allowances: NOX (in tons)		9,000
Natural gas (in decatherms)	436,000,000	40,000,000
Electricity Capacity (Gigawatt Months)	5,000,000
Oil (millions of gallons)	6,000,000
Duke Energy Ohio [Member]
Electricity-energy (Gigawatt-hours)	29,770,000,000	14,655,000,000
Emission allowances: NOX (in tons)		9,000
Natural gas (in decatherms)	131,000,000	2,000,000