Income Taxes (Narrative) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Estimated annual effective income tax rate	30.20%	25.60%
Tax Refund	$ 19.9
Decrease in income tax expense	1.2
Increase (decrease) in deferred tax liabilities	23.3
Additional tax decrease	1.2
Effective income tax rates	23.20%	26.00%
DP&L [Member]
Estimated annual effective income tax rate	28.80%	31.10%
Increase (decrease) in deferred tax liabilities	$ 21.3
Effective income tax rates	24.10%	31.30%