Income Taxes (Narrative) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Estimated annual effective income tax rate			30.70%	29.00%
Tax Refund	$ 19.9		$ 19.9
Decrease in income tax expense			1.2
Increase (decrease) in deferred tax liabilities			29.9
Additional tax decrease			1.2
Effective income tax rates	13.30%	51.00%	18.20%	37.40%
DP&L [Member]
Estimated annual effective income tax rate			29.60%	32.00%
Increase (decrease) in deferred tax liabilities			$ 24.0
Effective income tax rates	17.40%	33.30%	20.90%	32.20%