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Related Party Transactions (Details) - USD ($) $ in Millions		3 Months Ended		12 Months Ended
	Dec. 31, 2016	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Related Party Transaction [Line Items]
Charges for services provided		$ 13.9	$ 11.6
Sales to related party		1.0	1.2
Net payable to the Service Company	$ (2.0)	0.0		$ (2.0)
Investment in trust	$ 0.3	0.3		0.3
Debt Instrument, Interest Rate, Stated Percentage	3.02%
Due to Affiliate	$ (2.5)	(3.1)		(2.5)
Note to DPL Capital Trust II Maturing in September 2031 - 8.125% [Member]
Related Party Transaction [Line Items]
Note payable to trust	15.6	15.6		15.6
Prepaid Expenses and Other Current Assets [Member]
Related Party Transaction [Line Items]
Accounts Receivable, Related Parties, Current
Accrued Liabilities [Member]
Related Party Transaction [Line Items]
Net payable to the Service Company	(97.2)	(70.6)		(97.2)
Charges for health, welfare and benefit plans [Member] \| Subsidiary of Common Parent [Member]
Related Party Transaction [Line Items]
Transactions with other AES affiliates		4.2	4.1
THE DAYTON POWER AND LIGHT COMPANY [Member]
Related Party Transaction [Line Items]
Charges for services provided		13.0	8.9
Sales to related party		1.0	1.2
Premiums paid for insurance services provided by MVIC		(0.8)	(0.9)
Net payable to the Service Company	(2.0)	0.0		(2.0)
Gain on termination of contract		0.0	27.7
Notes Payable, Related Parties		(30.0)	(5.0)	(5.0)
Notes Payable, Related Parties	5.0	0.0		5.0
Due to Affiliate	(2.5)	5.0		(2.5)
THE DAYTON POWER AND LIGHT COMPANY [Member] \| Prepaid Expenses and Other Current Assets [Member]
Related Party Transaction [Line Items]
Accounts Receivable, Related Parties, Current	9.5	23.7		9.5
THE DAYTON POWER AND LIGHT COMPANY [Member] \| Accrued Liabilities [Member]
Related Party Transaction [Line Items]
Net payable to the Service Company
THE DAYTON POWER AND LIGHT COMPANY [Member] \| Insurance Proceeds Received [Member] \| Subsidiary of Common Parent [Member]
Related Party Transaction [Line Items]
Transactions with other AES affiliates		0.0	0.2
THE DAYTON POWER AND LIGHT COMPANY [Member] \| Charges for health, welfare and benefit plans [Member] \| Subsidiary of Common Parent [Member]
Related Party Transaction [Line Items]
Transactions with other AES affiliates		$ 4.1	$ 4.1