Consolidated Statements of Comprehensive Income/(Loss) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Net income / (loss)	$ 22.1	$ (1.0)	$ 105.4
Derivative activity:
Change in derivative fair value, net of income tax benefit/(expense)		0.0	(1.0)
Reclassification of earnings, net of income tax benefit/(expense)	(0.8)	(0.9)	(1.1)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives Related to Discontinued Operations, Net of Tax	0.0	0.0	(0.4)
Total change in fair value of derivatives	(0.8)	(0.9)	(2.5)
Pension and postretirement activity:
Prior service cost for the period, net of income tax benefit/(expense)	0.0	0.0	(0.1)
Net loss for the period, net of income tax benefit/(expense)	6.4	(8.8)	(3.4)
Reclassification to earnings, net of income tax benefit/(expense)	1.9	1.0	0.2
Total change in unfunded pension obligation	8.3	(7.8)	(3.3)
Other comprehensive income / (loss)	7.5	(8.7)	(5.8)
Net comprehensive income / (loss)	29.6	(9.7)	99.6
Income tax (expense)/benefit on unrealized gains (losses) related to derivative activity	0.0	0.0	0.1
Income tax (expense)/benefit on reclassification of earnings related to derivative activity		0.2	0.1
Income tax (expense)/benefit on prior service cost related to pension and postretirement activity	0.0	0.0	0.0
Income tax (expense)/benefit on net loss related to pension and postretirement activity	(1.8)	2.6	0.8
Tax expense (benefit)	0.5	5.5	20.3
Income tax (expense)/benefit on reclassification of earnings related to pension and postretirement activity		(0.3)	0.0
Other comprehensive loss before reclassifications	6.4	(8.8)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives Related to Discontinued Operations, Tax	0.0	0.0	(0.4)
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Pension and postretirement activity:
Other comprehensive income / (loss)	8.3	(7.8)
Other comprehensive loss before reclassifications	6.4	(8.8)
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member]
Pension and postretirement activity:
Other comprehensive income / (loss)	(0.8)	(0.9)
Other comprehensive loss before reclassifications	0.0	0.0
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Pension and postretirement activity:
Tax expense (benefit)	(0.6)	(0.3)	0.0
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member]
Pension and postretirement activity:
Tax expense (benefit)	0.2	0.2	0.1
THE DAYTON POWER AND LIGHT COMPANY [Member]
Net income / (loss)	47.1	51.1	124.9
Derivative activity:
Change in derivative fair value, net of income tax benefit/(expense)	0.0	(0.2)	(0.8)
Reclassification of earnings, net of income tax benefit/(expense)	0.0	0.6	(0.2)
Total change in fair value of derivatives	0.0	0.4	(1.0)
Pension and postretirement activity:
Net loss for the period, net of income tax benefit/(expense)	6.4	(8.7)	(3.6)
Reclassification to earnings, net of income tax benefit/(expense)	3.9	3.1	3.0
Total change in unfunded pension obligation	10.3	(5.6)	(0.6)
Other comprehensive income / (loss)	10.3	(5.2)	(1.6)
Net comprehensive income / (loss)	57.4	45.9	123.3
Income tax (expense)/benefit on unrealized gains (losses) related to derivative activity	0.0	(0.2)	0.3
Income tax (expense)/benefit on reclassification of earnings related to derivative activity		0.8	0.0
Income tax (expense)/benefit on net loss related to pension and postretirement activity	(1.8)	2.6	0.6
Tax expense (benefit)	(5.7)	(7.0)	0.6
Income tax (expense)/benefit on reclassification of earnings related to pension and postretirement activity		(0.9)	(0.5)
Other comprehensive loss before reclassifications		(8.9)
THE DAYTON POWER AND LIGHT COMPANY [Member] | Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Pension and postretirement activity:
Other comprehensive income / (loss)	10.3	(5.6)
Other comprehensive loss before reclassifications	6.4	(8.7)
THE DAYTON POWER AND LIGHT COMPANY [Member] | Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member]
Pension and postretirement activity:
Other comprehensive income / (loss)	0.0	0.4
Other comprehensive loss before reclassifications	0.0	(0.2)
THE DAYTON POWER AND LIGHT COMPANY [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Pension and postretirement activity:
Tax expense (benefit)	(1.1)	(0.9)	(0.5)
THE DAYTON POWER AND LIGHT COMPANY [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member]
Pension and postretirement activity:
Tax expense (benefit)	$ 0.0	$ 0.8	$ 0.0