Pension and Postretirement Benefits (Net Periodic Benefit Cost (Income)) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended			1 Months Ended	11 Months Ended	12 Months Ended		1 Months Ended	11 Months Ended		12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2011 Pension [Member]	Nov. 27, 2011 Pension [Member]	Dec. 31, 2012 Pension [Member]	Dec. 31, 2010 Pension [Member]	Dec. 31, 2011 Postretirement [Member]	Nov. 27, 2011 Postretirement [Member]		Dec. 31, 2012 Postretirement [Member]		Dec. 31, 2010 Postretirement [Member]		Dec. 31, 2012 DP&L [Member] Pension [Member]		Dec. 31, 2011 DP&L [Member] Pension [Member]		Dec. 31, 2010 DP&L [Member] Pension [Member]		Dec. 31, 2012 DP&L [Member] Postretirement [Member]	Dec. 31, 2011 DP&L [Member] Postretirement [Member]	Dec. 31, 2010 DP&L [Member] Postretirement [Member]
Service cost				$ 0.5	$ 4.5	$ 6.2	$ 4.8		$ 0.1		$ 0.1		$ 0.1		$ 6.2		$ 5.0		$ 4.8		$ 0.1	$ 0.1	$ 0.1
Interest cost				1.5	15.5	17.3	17.7	0.1	0.9		0.9		1.2		17.3		17.0		17.7		0.9	1.0	1.2
Expected return on assets				(2.0)	(22.5)	(22.7)	(22.4)		(0.3)	[1]	(0.3)	[1]	(0.3)	[1]	(22.7)	[1]	(24.5)	[1]	(22.4)	[1]	(0.3)	(0.3)	(0.3)
Actuarial (gain) / loss				0.4	7.6	5.0	7.2		(1.0)		(0.6)		(1.1)		8.8		8.0		7.2		(0.9)	(1.1)	(1.1)
Prior service cost				0.1	2.0	1.5	3.7	(0.1)	0.1				0.1		2.8		2.1		3.7		0.1	0.1	0.1
Net Periodic benefit cost / (income) before adjustments				0.5	7.1	7.3	11.0		(0.2)		0.1				12.4		7.6		11.0		(0.1)	(0.2)
Settlement Cost															0.6
Net periodic benefit cost / (income)															13.0		7.6		11.0
Period in which the difference between market related value of assets is calculated in years, max	five
Period in which the difference between actual and estimated asset returns in MRVA is calculated	three
Market related value of assets	$ 346.0	$ 335.0	$ 274.0

[1] (a) For purposes of calculating the expected return on pension plan assets under GAAP, the market-related value of assets (MRVA) is used. GAAP requires that the difference between actual plan asset returns and estimated plan asset returns be amortized into the MRVA equally over a period not to exceed five years. We use a methodology under which we include the difference between actual and estimated asset returns in the MRVA equally over a three year period. The MRVA used in the calculation of expected return on pension plan assets was approximately $346.0 million in 2012, $335.0 million in 2011, and $274.0 million in 2010.