Revenue (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Revenue from Contract with Customer, Excluding Assessed Tax	$ 667.6	$ 645.0	$ 720.6
Revenues	672.7	660.5	743.7
RTO Revenue	50.0	44.0	43.5
RTO Capacity Revenue	5.9	4.2	6.2
Contract with Customer, Asset, before Allowance for Credit Loss	61.5	70.1
Utility [Member]
Revenues	663.7	652.1	735.4
RTO Revenue	49.9	44.0	43.5
RTO Capacity Revenue	5.9	4.2	6.2
Corporate and Other
Revenues	13.2	12.9	12.6
RTO Revenue	0.1	0.0	0.0
RTO Capacity Revenue	0.0	0.0	0.0
Adjustments and Eliminations
Revenues	(4.2)	(4.5)	(4.3)
RTO Revenue	0.0	0.0	0.0
RTO Capacity Revenue	0.0	0.0	0.0
THE DAYTON POWER AND LIGHT COMPANY [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	658.6	636.6	712.2
Revenues	663.7	652.1	735.4
RTO Revenue	49.9	44.0	43.5
RTO Capacity Revenue	5.9	4.2	6.2
Contract with Customer, Asset, before Allowance for Credit Loss	60.8	69.2
Wholesale Revenue [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	18.8	10.1	16.2
Wholesale Revenue [Member] | Utility [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	19.5	11.0	17.2
Wholesale Revenue [Member] | Corporate and Other
Revenue from Contract with Customer, Excluding Assessed Tax	0.0	0.0	0.0
Wholesale Revenue [Member] | Adjustments and Eliminations
Revenue from Contract with Customer, Excluding Assessed Tax	(0.7)	(0.9)	(1.0)
Wholesale Revenue [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	19.5	11.0	17.2
Other Revenues [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	9.6	9.3	9.4
Other non-606 revenue	5.1	6.5	1.1
Other Revenues [Member] | Utility [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	0.0	0.0	0.0
Other non-606 revenue	5.1	6.5	1.2
Other Revenues [Member] | Corporate and Other
Revenue from Contract with Customer, Excluding Assessed Tax	9.6	9.3	9.4
Other non-606 revenue	3.5	3.6	3.2
Other Revenues [Member] | Adjustments and Eliminations
Revenue from Contract with Customer, Excluding Assessed Tax	0.0	0.0	0.0
Other non-606 revenue	(3.5)	(3.6)	(3.3)
Other Revenues [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Other non-606 revenue	5.1	6.5	1.2
Retail Revenue [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	583.3	577.4	645.3
Other non-606 revenue		9.0	22.0
Retail Revenue [Member] | Residential Revenue [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	364.9	362.3	403.5
Retail Revenue [Member] | Commercial Revenue [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	122.6	114.6	130.3
Retail Revenue [Member] | Industrial Revenue [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	57.5	51.2	55.3
Retail Revenue [Member] | Governmental Revenue [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	26.1	36.6	42.4
Retail Revenue [Member] | Other Revenues [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	12.2	12.7	13.8
Retail Revenue [Member] | Utility [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	583.3	577.4	645.3
Other non-606 revenue	0.0	9.0	22.0
Retail Revenue [Member] | Utility [Member] | Residential Revenue [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	364.9	362.3	403.5
Retail Revenue [Member] | Utility [Member] | Commercial Revenue [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	122.6	114.6	130.3
Retail Revenue [Member] | Utility [Member] | Industrial Revenue [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	57.5	51.2	55.3
Retail Revenue [Member] | Utility [Member] | Governmental Revenue [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	26.1	36.6	42.4
Retail Revenue [Member] | Utility [Member] | Other Revenues [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	12.2	12.7	13.8
Retail Revenue [Member] | Corporate, Non-Segment [Member]
Other non-606 revenue		0.0	0.0
Retail Revenue [Member] | Consolidation, Eliminations [Member]
Other non-606 revenue		0.0	0.0
Retail Revenue [Member] | Corporate and Other
Revenue from Contract with Customer, Excluding Assessed Tax	0.0	0.0	0.0
Retail Revenue [Member] | Corporate and Other | Residential Revenue [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	0.0	0.0	0.0
Retail Revenue [Member] | Corporate and Other | Commercial Revenue [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	0.0	0.0	0.0
Retail Revenue [Member] | Corporate and Other | Industrial Revenue [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	0.0	0.0	0.0
Retail Revenue [Member] | Corporate and Other | Governmental Revenue [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	0.0	0.0	0.0
Retail Revenue [Member] | Corporate and Other | Other Revenues [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	0.0	0.0	0.0
Retail Revenue [Member] | Adjustments and Eliminations
Revenue from Contract with Customer, Excluding Assessed Tax	0.0	0.0	0.0
Retail Revenue [Member] | Adjustments and Eliminations | Residential Revenue [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	0.0	0.0	0.0
Retail Revenue [Member] | Adjustments and Eliminations | Commercial Revenue [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	0.0	0.0	0.0
Retail Revenue [Member] | Adjustments and Eliminations | Industrial Revenue [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	0.0	0.0	0.0
Retail Revenue [Member] | Adjustments and Eliminations | Governmental Revenue [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	0.0	0.0	0.0
Retail Revenue [Member] | Adjustments and Eliminations | Other Revenues [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	$ 0.0	$ 0.0	$ 0.0