Condensed Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Net income	$ 21.0	$ 21.9	$ 41.4	$ (29.3)
Equity securities activity:
AOCI reclassed to Retained Earnings, net of tax	0.0	0.0	(1.0)	0.0
Total change in fair value of available-for-sale securities	0.0	0.1	(1.0)	0.3
Derivative activity:
Change in derivative fair value, net of income tax	0.1	1.4	0.4	12.1
Reclassification of earnings, net of income tax	(0.2)	(0.1)	(0.6)	(0.5)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives Related to Discontinued Operations, Net of Tax	0.0	(2.3)	2.8	(5.5)
Total change in fair value of derivatives	(0.1)	(1.0)	2.6	6.1
Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), Reclassification Adjustment from AOCI, before Tax	0.0	0.0	0.0	(0.3)
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, after Tax	0.0	0.0	0.0	(1.2)
Pension and postretirement activity:
Reclassification to earnings, net of income tax	0.1	0.0	0.4	0.9
Total change in unfunded pension obligation	0.1	0.0	0.4	(0.6)
Other comprehensive income / (loss)	0.0	(0.9)	2.0	5.8
Net comprehensive income / (loss)	21.0	21.0	43.4	(23.5)
Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, after Tax	0.0	0.1	0.0	0.4
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax	0.0	0.0	0.0	0.1
THE DAYTON POWER AND LIGHT COMPANY [Member]
Net income	31.2	29.3	61.9	3.6
Equity securities activity:
AOCI reclassed to Retained Earnings, net of tax	0.0	0.0	(1.1)	0.0
Total change in fair value of available-for-sale securities	0.0	0.1	(1.1)	0.3
Derivative activity:
Change in derivative fair value, net of income tax	0.0	1.4	0.5	12.1
Reclassification of earnings, net of income tax	(0.2)	(0.2)	(0.5)	(0.5)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives Related to Discontinued Operations, Net of Tax	0.0	(2.2)	0.0	(5.5)
Total change in fair value of derivatives	(0.2)	(1.0)	0.0	6.1
Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), Reclassification Adjustment from AOCI, before Tax	0.0	0.0	0.0	(1.1)
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, after Tax	0.0	0.0	0.0	(0.5)
Pension and postretirement activity:
Reclassification to earnings, net of income tax	0.9	0.7	2.5	3.8
Total change in unfunded pension obligation	0.9	0.7	2.5	2.2
Other comprehensive income / (loss)	0.7	(0.2)	1.4	8.6
Net comprehensive income / (loss)	31.9	29.1	63.3	12.2
Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, after Tax	0.0	0.1	0.0	0.4
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax	$ 0.0	$ 0.0	0.0	$ 0.1
Gains / (losses) on available-for-sale securities [Member]
Equity securities activity:
AOCI reclassed to Retained Earnings, net of tax			(1.0)
Pension and postretirement activity:
Other comprehensive income / (loss)			(1.0)
Gains / (losses) on available-for-sale securities [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Equity securities activity:
AOCI reclassed to Retained Earnings, net of tax			(1.1)
Pension and postretirement activity:
Other comprehensive income / (loss)			$ (1.1)