Overview and Summary of Significant Accounting Policies (Summary of Property, Plant, and Equipment) (Details) (USD $) In Millions, unless otherwise specified	1 Months Ended	11 Months Ended	12 Months Ended
	Dec. 31, 2011	Nov. 27, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Public Utility, Property, Plant and Equipment [Line Items]
Total property, plant and equipment in service	$ 2,360.3		$ 2,590.4	$ 2,360.3
Total property, plant and equipment in service, Composite Rate			4.80%	5.80%	2.60%
Public Utilities, Allowance for Funds Used During Construction, Capitalized Interest	0.5	3.9	4.0		3.4
DP&L [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Total property, plant and equipment in service	5,277.9		5,249.0	5,277.9
Total property, plant and equipment in service, Composite Rate			4.20%	2.50%	2.60%
Public Utilities, Allowance for Funds Used During Construction, Capitalized Interest			4.0	4.4	3.4
Regulated Operation [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Transmission	189.5		208.9	189.5
Distribution	803.0		935.0	803.0
General	26.3		50.6	26.3
Non-depreciable	59.7		60.0	59.7
Total property, plant and equipment in service	1,078.5		1,254.5	1,078.5
Transmission, Composite Rate	4.80%		4.40%	4.80%
Distribution, Composite Rate			5.40%	5.80%
General, Composite Rate			10.80%	13.10%
Regulated Operation [Member] | DP&L [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Transmission	367.5		380.9	367.5
Distribution	1,371.5		1,480.7	1,371.5
General	84.8		100.0	84.8
Non-depreciable	59.7		60.1	59.7
Total property, plant and equipment in service	1,883.5		2,021.7	1,883.5
Transmission, Composite Rate	2.40%		2.40%	2.40%
Distribution, Composite Rate			3.40%	3.40%
General, Composite Rate			5.40%	4.10%
Unregulated Operation [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Production / Generation	1,248.0		1,299.7	1,248.0
Other	14.4		16.6	14.4
Non-depreciable	19.4		19.6	19.4
Total property, plant and equipment in service	1,281.8		1,335.9	1,281.8
Production/Generation, Composite Rate			4.40%	6.00%
Other, Composite Rate			11.60%	10.10%
Unregulated Operation [Member] | DP&L [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Production / Generation	3,377.9		3,210.8	3,377.9
Non-depreciable	16.5		16.5	16.5
Total property, plant and equipment in service	$ 3,394.4		$ 3,227.3	$ 3,394.4
Production/Generation, Composite Rate			4.90%	2.20%