Revenue (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Revenue from Contract with Customer, Excluding Assessed Tax	$ 743.8
Revenues	775.9
RTO Revenue	43.2
RTO Capacity Revenue	14.4
Contract with Customer, Asset, Gross	72.6	$ 63.0
Utility [Member]
Revenues	738.7
RTO Revenue	43.1
RTO Capacity Revenue	7.8
Corporate, Non-Segment [Member]
Revenues	41.0
RTO Revenue	0.1
RTO Capacity Revenue	6.6
Consolidation, Eliminations [Member]
Revenues	(3.8)
RTO Revenue	0.0
RTO Capacity Revenue	0.0
THE DAYTON POWER AND LIGHT COMPANY [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	706.6
Revenues	738.7
RTO Revenue	43.1
RTO Capacity Revenue	7.8
Contract with Customer, Asset, Gross	70.1	$ 62.1
Wholesale Revenue [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	52.0
Wholesale Revenue [Member] | Utility [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	29.9
Wholesale Revenue [Member] | Corporate, Non-Segment [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	22.1
Wholesale Revenue [Member] | Consolidation, Eliminations [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	0.0
Wholesale Revenue [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	29.9
Other Revenues [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	9.4
Other non-606 revenue	0.0
Other Revenues [Member] | Utility [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	0.0
Other non-606 revenue	0.0
Other Revenues [Member] | Corporate, Non-Segment [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	9.4
Other non-606 revenue	2.8
Other Revenues [Member] | Consolidation, Eliminations [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	0.0
Other non-606 revenue	(2.8)
Retail Revenue [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	624.8
Other non-606 revenue	32.1
Retail Revenue [Member] | Utility [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	625.8
Other non-606 revenue	32.1
Retail Revenue [Member] | Corporate, Non-Segment [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	0.0
Other non-606 revenue	0.0
Retail Revenue [Member] | Consolidation, Eliminations [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	(1.0)
Other non-606 revenue	0.0
Retail Revenue [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	625.8
Other non-606 revenue	$ 32.1