Acquisitions and Sales of Other Assets (Megawatts per hour sold) (Details)	6 Months Ended
	Jun. 30, 2012 MWh
Summer off-peak hours	800
Summer on-peak hours	475
Winter off-peak hours	225
Winter on-peak hours	25
Duke Energy Carolinas [Member]
Summer off-peak hours	300
Summer on-peak hours	150
Winter off-peak hours	225
Winter on-peak hours	25
Progress Energy Carolinas [Member]
Summer off-peak hours	500
Summer on-peak hours	325
Winter off-peak hours	0
Winter on-peak hours	0