Regulatory Matters (Schedule of MISO Exit fees)(Details) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2012
Restructuring Liability, beginning balance	$ 32
Cash Reductions	(8)
Restructuring Reserve, Period Expense	(1)
Restructuring Liability, ending balance	23
Duke Energy Ohio [Member] | Regional Transmission Organization Realignment [Member]
Restructuring Liability, beginning balance	110
Cash Reductions	(15)
Restructuring Reserve Period Deferral	2
Restructuring Liability, ending balance	$ 97