Business Combination (Change to Preliminary Purchase Price Allocation Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2012
Deferred Income Tax Effect [Member]
Goodwill, Purchase Accounting Adjustments	$ (87.0)
Total Adjustment [Member] | Deferred Income Tax Effect [Member]
Goodwill, Purchase Accounting Adjustments	7.5
Total Adjustment [Member] | Change Before Deferred Income Tax Effect [Member]
Goodwill, Purchase Accounting Adjustments	(94.5)
Other Deferred Liabilities [Member] | Change Before Deferred Income Tax Effect [Member]
Goodwill, Purchase Accounting Adjustments	1.0
Taxes Payable [Member] | Deferred Income Tax Effect [Member]
Goodwill, Purchase Accounting Adjustments	(16.0)	[1]
Taxes Payable [Member] | Change Before Deferred Income Tax Effect [Member]
Goodwill, Purchase Accounting Adjustments	13.1	[1]
Regulatory Assets [Member] | Change Before Deferred Income Tax Effect [Member]
Goodwill, Purchase Accounting Adjustments	15.4	[2]
Deferred Tax Liabilities [Member] | Deferred Income Tax Effect [Member]
Goodwill, Purchase Accounting Adjustments	(20.7)	[3]
Out Of Market Coal Contract [Member] | Deferred Income Tax Effect [Member]
Goodwill, Purchase Accounting Adjustments	12.0	[4]
Out Of Market Coal Contract [Member] | Change Before Deferred Income Tax Effect [Member]
Goodwill, Purchase Accounting Adjustments	(34.2)	[4]
DPLER Intangibles [Member] | Deferred Income Tax Effect [Member]
Goodwill, Purchase Accounting Adjustments	6.7	[5]
DPLER Intangibles [Member] | Change Before Deferred Income Tax Effect [Member]
Goodwill, Purchase Accounting Adjustments	(19.1)	[5]
Property, Plant And Equipment [Member] | Deferred Income Tax Effect [Member]
Goodwill, Purchase Accounting Adjustments	25.5	[6]
Property, Plant And Equipment [Member] | Change Before Deferred Income Tax Effect [Member]
Goodwill, Purchase Accounting Adjustments	$ (70.7)	[6]

[1] (f) related to the final 2011 DPL Inc. standalone federal tax return.

[2] (e) related to the increase in deferred taxes discussed in (d) above.

[3] (d) related to an assessment of our overall deferred tax liabilities on regulated property, plant and equipment.

[4] (c) related to a change in certain assumptions related to an out of market coal contract.

[5] (b) related to refined market and contractual information.

[6] (a) related to refined information associated with certain contractual arrangements, growth and ancillary revenue assumptions.