Regulatory Matters (Schedule of MISO Exit fees)(Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2012
Restructuring Liability, beginning balance	$ 32
Cash Reductions	39
Restructuring Reserve, Period Expense	118
Restructuring Liability, ending balance	111
Duke Energy Ohio [Member] | Regional Transmission Organization Realignment [Member]
Restructuring Liability, beginning balance	110
Cash Reductions	(18)
Restructuring Reserve Period Deferral	3
Restructuring Liability, ending balance	$ 95