Pension and Postretirement Benefits (Fair Value Measurements for Postretirement Plan Assets) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012		Dec. 31, 2011		Nov. 27, 2011	Dec. 31, 2010
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 361.4
DP&L [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	361.4
Postretirement [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	4.2		4.5		4.5	4.8
Postretirement [Member] | DP&L [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	4.2		4.5			4.8
JP Morgan Core Bond Fund [Member] | Postretirement [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	4.2	[1]	4.5	[1]
JP Morgan Core Bond Fund [Member] | Postretirement [Member] | DP&L [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	4.2	[1]	4.5	[1]
Level 2 [Member] | JP Morgan Core Bond Fund [Member] | Postretirement [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	4.2	[1]	4.5	[1]
Level 2 [Member] | JP Morgan Core Bond Fund [Member] | Postretirement [Member] | DP&L [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 4.2	[1]	$ 4.5	[1]

[1] (a) This category includes investments in U.S. government obligations and mortgage-backed and asset-backed securities. The funds are valued using the net asset value method in which an average of the market prices for the underlying investments is used to value the fund.