Overview and Summary of Significant Accounting Policies (Narrative) (Details) $ in Millions			12 Months Ended
	Jan. 31, 2020	Jan. 01, 2018 USD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($) mi² segment customer	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Jan. 31, 2021 employee
Significant Accounting Policies [Line Items]
Other Investments				$ 0.2	$ 0.2
Cash and Cash Equivalents, at Carrying Value				25.4	36.5
Restricted Cash and Cash Equivalents, Current				0.1	10.5
Capitalized Software, estimated amortization expense for year after next				$ 2.2
Number of reportable segments | segment				1
Service area, square miles | mi²				6,000
Capitalized interest for unregulated generation property				$ 3.0	$ 3.2	$ 0.5
Straight-line depreciation average annual composite basis (percent)				3.80%	4.00%	4.30%
Depreciation and amortization				$ 73.3	$ 72.3	$ 76.2
Insurance and claims costs				3.2	4.5
Insurance costs below coverage thresholds of third-party providers				11.1	3.3
Employees under collective bargaining agreement (percent)	58.00%
Capitalized Computer Software, Amortization				3.3	4.4	6.5
Capitalized Software, estimated amortization over remaining useful life				10.7
Capitalized Software, estimated amortization expense for next twelve months				3.0
Capitalized Software, estimated amortization expense for three years in the future				2.0
Capitalized Software, estimated amortization expense for four years in the future				1.8
Capitalized Software, estimated amortization expense for five years in the future				1.7
AOCI reclassed to Retained Earnings before tax		$ 1.6
AOCI reclassed to Retained Earnings, net of tax		1.0
Restricted Cash and Cash Equivalents				25.5	47.0	111.7	$ 24.9
Carrying Value				1,565.3	1,445.6
Other Assets, Noncurrent				24.6	20.0
Prepaid Implementation Costs for Software as a Service
Significant Accounting Policies [Line Items]
Other Assets, Noncurrent				4.1
THE DAYTON POWER AND LIGHT COMPANY [Member]
Significant Accounting Policies [Line Items]
Cash and Cash Equivalents, at Carrying Value				11.7	10.8
Restricted Cash and Cash Equivalents, Current				0.1	10.5
Payments of Ordinary Dividends, Common Stock				42.7	43.8	43.8
Capitalized Software, estimated amortization expense for year after next				$ 2.1
Approximate number of retail customers | customer				531,000
Service area, square miles | mi²				6,000
Capitalized interest for unregulated generation property				$ 3.0	$ 3.2	$ 0.5
Straight-line depreciation average annual composite basis (percent)				2.80%	2.90%	3.00%
Depreciation and amortization				$ 71.8	$ 70.8	$ 74.5
Insurance costs below coverage thresholds of third-party providers				3.5	3.3
Percentage Of Employees Under Collective Bargaining Agreement	58.00%
Capitalized Computer Software, Amortization					3.2	4.3	6.3
Capitalized Software, estimated amortization over remaining useful life					10.2
Capitalized Software, estimated amortization expense for next twelve months				2.9
Capitalized Software, estimated amortization expense for three years in the future				1.9
Capitalized Software, estimated amortization expense for four years in the future				1.7
Capitalized Software, estimated amortization expense for five years in the future				1.6
AOCI reclassed to Retained Earnings before tax		1.7
AOCI reclassed to Retained Earnings, net of tax		$ 1.1
Restricted Cash and Cash Equivalents				11.8	21.3	66.2	$ 5.6
Carrying Value				1,544.0	1,425.4
Other Assets, Noncurrent				24.0	19.6
THE DAYTON POWER AND LIGHT COMPANY [Member] | Prepaid Implementation Costs for Software as a Service
Significant Accounting Policies [Line Items]
Other Assets, Noncurrent				4.1
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								631
Entity Number of Full Time Employees | employee								512
Subsequent Event [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Significant Accounting Policies [Line Items]
Entity number of employees | employee								631
Entity Number of Full Time Employees | employee								512
Electric Generation, Transmission and Distribution Equipment [Member]
Significant Accounting Policies [Line Items]
Depreciation and amortization				70.0	67.9	69.7
Electric Generation, Transmission and Distribution Equipment [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Significant Accounting Policies [Line Items]
Depreciation and amortization				68.6	66.5	68.2
Pension [Member]
Significant Accounting Policies [Line Items]
Service cost				3.7	3.7	6.1
Interest cost				11.8	14.9	13.8
Pension [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Significant Accounting Policies [Line Items]
Service cost				3.7	3.7	6.1
Interest cost				$ 11.8	$ 14.9	13.8
Pension [Member] | Forecast [Member]
Significant Accounting Policies [Line Items]
Service cost			$ 5.3
Pension [Member] | Forecast [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Significant Accounting Policies [Line Items]
Service cost			$ 5.3
Adjustments for New Accounting Pronouncement [Member]
Significant Accounting Policies [Line Items]
AOCI reclassed to Retained Earnings before tax						1.6
AOCI reclassed to Retained Earnings, net of tax						$ 1.0