Common Shareholders' Equity (Details) (USD $) In Millions, except Share data, unless otherwise specified	1 Months Ended		12 Months Ended			9 Months Ended
	Mar. 31, 2012	Jun. 30, 2011	Dec. 31, 2011	Sep. 30, 2012	Dec. 05, 2011	Sep. 30, 2012 DP&L [Member]
Common stock, shares authorized				1,500		250,000,000
Common stock, shares outstanding				1		41,172,173
Dividends, Preferred Stock, Cash						$ 0.2
Warrants exercised	1,000,000	700,000
Proceeds from exercise of warrants		14.7
Warrant exercise price			21.00
PUCO Meger Equity Ratio Approval						50.00%
ESOP Loan Repayment To Employer					68.2
Difference between strike price and merger price			9.00
Financial Instruments Subject to Mandatory Redemption, Settlement Terms, Excess of Liabilities over Assets			9.0
Acquisition cost per share			$ 30.00
Cash Dividends Paid to Parent Company						$ 75.0