Income Taxes (Narrative) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Estimated annual effective income tax rate			(2.20%)	33.20%
Decrease in income tax expense	$ 16.7
Increase in deferred state income taxes			3.6
Decrease in other estimated tax liabilities			0.2
Increase (decrease) in deferred tax liabilities	25.4		19.1
Additional tax decrease	0.9		0.9
Effective income tax rates	(1.20%)	29.90%	(2.30%)	32.90%
DP&L [Member]
Estimated annual effective income tax rate			30.70%	33.10%
Decrease in income tax expense	1.3
Decrease in other estimated tax liabilities			0.3
Increase (decrease) in deferred tax liabilities	4.8		6.3
Additional tax decrease	$ 9.3		$ 9.3
Effective income tax rates	(138.30%)	29.60%	40.30%	32.00%