Common Shareholders' Equity (Details) (USD $) In Millions, except Share data, unless otherwise specified	1 Months Ended	12 Months Ended
	Jun. 30, 2011	Dec. 31, 2011	Mar. 31, 2012
Common stock, shares authorized		1,500	1,500
Common stock, shares outstanding		1	1
Warrants exercised	700,000
Proceeds from exercise of warrants	$ 14.7
Warrant exercise price		21.00
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
DP&L [Member]
Common stock, shares authorized			250,000,000
Common stock, shares outstanding			41,172,173
Acquisition cost per share		$ 30