Income Taxes (Narrative) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Estimated annual effective income tax rate			29.00%	33.70%
Increase in income tax expense	$ 3.7		$ 3.9
Increase in deferred state income taxes	3.6		3.6
Decrease in other estimated tax liabilities	0.1		0.3
Increase (decrease) in deferred tax liabilities	44.1		11.5
Effective income tax rates	64.00%	34.00%	38.10%	35.30%
DP&L [Member]
Estimated annual effective income tax rate			32.00%	33.50%
Increase (decrease) in deferred tax liabilities	5.2		1.5
Additional tax expense	$ 0.2		$ 0.3
Effective income tax rates	33.30%	33.60%	32.20%	33.80%