Pension and Postretirement Benefits (Fair Value Measurements for Pension 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]
Total Equity Securities	$ 101.8
Total Debt Securities	208.7
Total Other Investments	37.0
Total Pension Plan Assets	361.4
DP&L [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Equity Securities	101.8
Total Debt Securities	208.7
Total Other Investments	37.0
Total Pension Plan Assets	361.4
Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Equity Securities		104.9
Total Debt Securities		130.8
Total Other Investments		72.2
Total Pension Plan Assets	361.4	335.9	335.8	291.8
Pension [Member] | DP&L [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Equity Securities		104.9
Total Debt Securities		130.8
Total Other Investments		72.2
Total Pension Plan Assets	361.4	335.9		291.8
Level 1 [Member] | Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Pension Plan Assets	13.9	28.0
Level 1 [Member] | Pension [Member] | DP&L [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Pension Plan Assets	13.9	28.0
Level 2 [Member] | Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Equity Securities	101.8	104.9
Total Debt Securities	208.7	130.8
Total Pension Plan Assets	310.5	235.7
Level 2 [Member] | Pension [Member] | DP&L [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Equity Securities	101.8	104.9
Total Debt Securities	208.7	130.8
Total Pension Plan Assets	310.5	235.7
Level 3 [Member] | Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Other Investments	37.0	72.2
Total Pension Plan Assets	37.0	72.2
Level 3 [Member] | Pension [Member] | DP&L [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Other Investments	37.0	72.2
Total Pension Plan Assets	37.0	72.2
Small/Mid Cap Equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Equity Securities	14.3
Small/Mid Cap Equity [Member] | DP&L [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Equity Securities	14.3
Small/Mid Cap Equity [Member] | Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Equity Securities		16.2
Small/Mid Cap Equity [Member] | Pension [Member] | DP&L [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Equity Securities		16.2
Small/Mid Cap Equity [Member] | Level 2 [Member] | Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Equity Securities	14.3	16.2
Small/Mid Cap Equity [Member] | Level 2 [Member] | Pension [Member] | DP&L [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Equity Securities	14.3	16.2
Large Cap Equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Equity Securities	50.5
Large Cap Equity [Member] | DP&L [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Equity Securities	50.5
Large Cap Equity [Member] | Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Equity Securities		54.5
Large Cap Equity [Member] | Pension [Member] | DP&L [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Equity Securities		54.5
Large Cap Equity [Member] | Level 2 [Member] | Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Equity Securities	50.5	54.5
Large Cap Equity [Member] | Level 2 [Member] | Pension [Member] | DP&L [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Equity Securities	50.5	54.5
International Equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Equity Securities	37.0
International Equity [Member] | DP&L [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Equity Securities	37.0
International Equity [Member] | Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Equity Securities		34.2
International Equity [Member] | Pension [Member] | DP&L [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Equity Securities		34.2
International Equity [Member] | Level 2 [Member] | Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Equity Securities	37.0	34.2
International Equity [Member] | Level 2 [Member] | Pension [Member] | DP&L [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Equity Securities	37.0	34.2
Emerging Markets Debt [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Debt Securities	7.4
Emerging Markets Debt [Member] | DP&L [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Debt Securities	7.4
Emerging Markets Debt [Member] | Level 2 [Member] | Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Debt Securities	7.4
Emerging Markets Debt [Member] | Level 2 [Member] | Pension [Member] | DP&L [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Debt Securities	7.4
High Yield Bond [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Debt Securities	12.7
High Yield Bond [Member] | DP&L [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Debt Securities	12.7
High Yield Bond [Member] | Level 2 [Member] | Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Debt Securities	12.7
High Yield Bond [Member] | Level 2 [Member] | Pension [Member] | DP&L [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Debt Securities	12.7
Long Duration Fund [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Debt Securities	188.6
Long Duration Fund [Member] | DP&L [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Debt Securities	188.6
Long Duration Fund [Member] | Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Debt Securities		130.8
Long Duration Fund [Member] | Pension [Member] | DP&L [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Debt Securities		130.8
Long Duration Fund [Member] | Level 2 [Member] | Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Debt Securities	188.6	130.8
Long Duration Fund [Member] | Level 2 [Member] | Pension [Member] | DP&L [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Debt Securities	188.6	130.8
Cash [Member]
Defined Benefit Plan Disclosure [Line Items]
Cash	13.9
Cash [Member] | DP&L [Member]
Defined Benefit Plan Disclosure [Line Items]
Cash	13.9
Cash [Member] | Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Cash		28.0
Cash [Member] | Pension [Member] | DP&L [Member]
Defined Benefit Plan Disclosure [Line Items]
Cash		28.0
Cash [Member] | Level 1 [Member] | Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Cash	13.9	28.0
Cash [Member] | Level 1 [Member] | Pension [Member] | DP&L [Member]
Defined Benefit Plan Disclosure [Line Items]
Cash	13.9	28.0
Limited Partnership Interest [Member] | Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Other Investments		0.8
Total Pension Plan Assets	0	0.8	0.9	2.8
Limited Partnership Interest [Member] | Pension [Member] | DP&L [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Other Investments		0.8
Total Pension Plan Assets	0	0.8		2.8
Limited Partnership Interest [Member] | Level 3 [Member] | Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Other Investments		0.8
Limited Partnership Interest [Member] | Level 3 [Member] | Pension [Member] | DP&L [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Other Investments		0.8
Common Collective Fund [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Other Investments	37.0
Common Collective Fund [Member] | DP&L [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Other Investments	37.0
Common Collective Fund [Member] | Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Other Investments		71.4
Total Pension Plan Assets	37.0	71.4	71.3	57.4
Common Collective Fund [Member] | Pension [Member] | DP&L [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Other Investments		71.4
Total Pension Plan Assets	37.0	71.4		57.4
Common Collective Fund [Member] | Level 3 [Member] | Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Other Investments	37.0	71.4
Common Collective Fund [Member] | Level 3 [Member] | Pension [Member] | DP&L [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Other Investments	$ 37.0	$ 71.4