Overview and Summary of Significant Accounting Policies (Narrative) (Details) $ in Millions		12 Months Ended
	Jan. 31, 2016 employee	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($) mi² customer generating_facility segment	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Significant Accounting Policies [Line Items]
Number of reportable segments | segment			1
Service area, square miles | mi²			6,000
Number of coal fired power plants | generating_facility			5
Electric Generation supplied to customers (percent)			1.00
Electric Generation through competitive bid (percent)			100.00%
Approximate number of DPLER customers			125,000
DPLER Customers That Are DPL Electric Distribution Customers			110,000
Capitalized interest for unregulated generation propety			$ 2.0	$ 1.5	$ 1.5
Straight-line depreciation average annual composite basis (percent)			4.60%	5.30%	5.80%
Depreciation and amortization			$ 134.6	$ 135.6	$ 129.2
Insurance and claims costs			5.9	6.4
Insurance costs below coverage thresholds of third-party providers			13.7	15.6
Investment in trust			0.3	0.3
Deferred financing costs that will be reclassed and deducted from debt amount			$ 16.1
THE DAYTON POWER AND LIGHT COMPANY [Member]
Significant Accounting Policies [Line Items]
Approximate number of retail customers | customer			517,000
Service area, square miles | mi²			6,000
Number of coal fired power plants | generating_facility			5
Electric Generation supplied to customers (percent)			1.00
Electric Generation through competitive bid (percent)			100.00%
Capitalized interest for unregulated generation propety			$ 2.0	$ 1.5	$ 1.5
Straight-line depreciation average annual composite basis (percent)			2.60%	2.80%	4.40%
Depreciation and amortization			$ 138.2	$ 144.8	$ 140.2
Insurance costs below coverage thresholds of third-party providers			13.7	15.6
Deferred financing costs that will be reclassed and deducted from debt amount			6.3
Note to DPL Capital Trust II Maturing in 2031 - 8.125% [Member]
Significant Accounting Policies [Line Items]
Note payable to trust			15.6	15.6
Subsequent Event [Member]
Significant Accounting Policies [Line Items]
Entity number of employees | employee	1,219
Employees under collective bargaining agreement (percent)	60.00%
Subsequent Event [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Significant Accounting Policies [Line Items]
Entity number of employees | employee	1,189
Percentage Of Employees Under Collective Bargaining Agreement	61.00%
Electric Generation, Transmission and Distribution Equipment [Member]
Significant Accounting Policies [Line Items]
Depreciation and amortization			125.9	128.1	120.9
Electric Generation, Transmission and Distribution Equipment [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Significant Accounting Policies [Line Items]
Depreciation and amortization			132.7	141.6	136.5
Pension [Member]
Significant Accounting Policies [Line Items]
Service cost			7.1	5.9	7.2
Interest cost			17.3	17.5	15.6
Pension [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Significant Accounting Policies [Line Items]
Service cost			7.1	5.9	7.2
Interest cost			17.3	17.5	15.6
Pension [Member] | Scenario, Forecast [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Significant Accounting Policies [Line Items]
Service cost		$ 0.4
Interest cost		3.2
Postretirement [Member]
Significant Accounting Policies [Line Items]
Service cost			0.2	0.2	0.2
Interest cost			0.6	0.8	0.8
Postretirement [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Significant Accounting Policies [Line Items]
Service cost			0.2	0.2	0.2
Interest cost			0.6	$ 0.8	$ 0.8
Disaggregated Rate Approach [Member] | Scenario, Forecast [Member]
Significant Accounting Policies [Line Items]
Service cost		5.9
Interest cost		15.4
Disaggregated Rate Approach [Member] | Scenario, Forecast [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Significant Accounting Policies [Line Items]
Service cost		5.9
Interest cost		15.4
Disaggregated Rate Approach [Member] | Pension [Member] | Scenario, Forecast [Member]
Significant Accounting Policies [Line Items]
Service cost		5.7
Interest cost		14.8
Disaggregated Rate Approach [Member] | Pension [Member] | Scenario, Forecast [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Significant Accounting Policies [Line Items]
Service cost		5.7
Interest cost		14.8
Disaggregated Rate Approach [Member] | Postretirement [Member] | Scenario, Forecast [Member]
Significant Accounting Policies [Line Items]
Service cost		0.2
Interest cost		0.6
Disaggregated Rate Approach [Member] | Postretirement [Member] | Scenario, Forecast [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Significant Accounting Policies [Line Items]
Service cost		0.2
Interest cost		0.6
Aggregate Rate Approach [Member] | Scenario, Forecast [Member]
Significant Accounting Policies [Line Items]
Service cost		6.3
Interest cost		18.6
Aggregate Rate Approach [Member] | Scenario, Forecast [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Significant Accounting Policies [Line Items]
Service cost		6.3
Interest cost		18.6
Aggregate Rate Approach [Member] | Pension [Member] | Scenario, Forecast [Member]
Significant Accounting Policies [Line Items]
Service cost		6.1
Interest cost		17.9
Aggregate Rate Approach [Member] | Pension [Member] | Scenario, Forecast [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Significant Accounting Policies [Line Items]
Service cost		6.1
Interest cost		17.9
Aggregate Rate Approach [Member] | Postretirement [Member] | Scenario, Forecast [Member]
Significant Accounting Policies [Line Items]
Service cost		0.2
Interest cost		0.7
Aggregate Rate Approach [Member] | Postretirement [Member] | Scenario, Forecast [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Significant Accounting Policies [Line Items]
Service cost		0.2
Interest cost		0.7
Impact of Change [Member] | Scenario, Forecast [Member]
Significant Accounting Policies [Line Items]
Service cost		(0.4)
Interest cost		(3.2)
Impact of Change [Member] | Scenario, Forecast [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Significant Accounting Policies [Line Items]
Service cost		(0.4)
Interest cost		(3.2)
Impact of Change [Member] | Pension [Member] | Scenario, Forecast [Member]
Significant Accounting Policies [Line Items]
Service cost		(0.4)
Interest cost		(3.1)
Impact of Change [Member] | Pension [Member] | Scenario, Forecast [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Significant Accounting Policies [Line Items]
Service cost		(0.4)
Interest cost		(3.1)
Impact of Change [Member] | Postretirement [Member] | Scenario, Forecast [Member]
Significant Accounting Policies [Line Items]
Service cost		0.0
Interest cost		(0.1)
Impact of Change [Member] | Postretirement [Member] | Scenario, Forecast [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Significant Accounting Policies [Line Items]
Service cost		0.0
Interest cost		$ (0.1)
Line of Credit [Member]
Significant Accounting Policies [Line Items]
Deferred financing costs that will be reclassed and deducted from debt amount			3.1
Line of Credit [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Significant Accounting Policies [Line Items]
Deferred financing costs that will be reclassed and deducted from debt amount			$ 0.7