Equity (Narrative) (Details) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2016 USD ($) fiscal_quarter $ / shares shares	Dec. 31, 2015 USD ($) $ / shares shares	Dec. 31, 2014 USD ($)	Jan. 01, 2016 USD ($)
Class of Stock [Line Items]
Preferred stock dividends, number of quarters in arrears to trigger permission to elect board members | fiscal_quarter	4
Maximum leverage ratio to allow distribution to shareholder	0.67
Minimum coverage ratio to allow distribution to shareholder	2.50
Retained earnings / (deficit) | $	$ (2,820.9)	$ (2,335.7)
Common stock, shares authorized | shares	1,500	1,500
Common stock, shares outstanding | shares	1	1
Leverage Ratio	1.45
Accounts Payable, Related Parties, Current | $	$ 2.0	$ 0.5
PUCO Equity Ratio	32.00%
THE DAYTON POWER AND LIGHT COMPANY [Member]
Class of Stock [Line Items]
Preferred stock dividends, number of quarters in arrears to trigger permission to elect board members | fiscal_quarter	4
Retained earnings / (deficit) | $	$ (406.3)	$ 437.3
Common stock, shares authorized | shares	250,000,000	250,000,000
Common stock, shares outstanding | shares	41,172,173	41,172,173
PUCO Meger Equity Ratio Approval	50.00%
Accounts Payable, Related Parties, Current | $	$ 2.0	$ 0.5
PUCO Equity Ratio	32.00%
$100 Redeemable Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock par value	$ 100
Preferred stock shares outstanding | shares	228,508
$100 Redeemable Preferred Stock [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Class of Stock [Line Items]
Preferred stock par value	$ 100
Preferred stock shares authorized | shares	4,000,000
Preferred stock shares outstanding | shares		228,508
$25 Redeemable Preferred Stock [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Class of Stock [Line Items]
Preferred stock par value	$ 25
Preferred stock shares authorized | shares	4,000,000
DP&L Series A [Member]
Class of Stock [Line Items]
Temporary Equity, Preferred Stock Rate	3.75%	3.75%
Temporary Equity, Redemption Price Per Share	$ 102.50	$ 102.50
DP&L Series A [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Class of Stock [Line Items]
Temporary Equity, Preferred Stock Rate	3.75%	3.75%
Temporary Equity, Redemption Price Per Share	$ 102.50	$ 102.50
DP&L Series B [Member]
Class of Stock [Line Items]
Temporary Equity, Preferred Stock Rate	3.75%	3.75%
Temporary Equity, Redemption Price Per Share	$ 103.00	$ 103.00
DP&L Series B [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Class of Stock [Line Items]
Temporary Equity, Preferred Stock Rate	3.75%	3.75%
Temporary Equity, Redemption Price Per Share	$ 103.00	$ 103.00
DP&L Series C [Member]
Class of Stock [Line Items]
Temporary Equity, Preferred Stock Rate	3.90%	3.90%
Temporary Equity, Redemption Price Per Share	$ 101.00	$ 101.00
DP&L Series C [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Class of Stock [Line Items]
Temporary Equity, Preferred Stock Rate	3.90%	3.90%
Temporary Equity, Redemption Price Per Share	$ 101.00	$ 101.00
Subsidiary of Common Parent [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Class of Stock [Line Items]
Accounts Payable, Related Parties, Current | $				$ 7.5
Equity Settlement of Related Party Payable | $	$ 7.5	$ 0.0	$ 0.0