Condensed Consolidated Statements of Cash Flows - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Cash flows from operating activities:
Net income	$ (29.3)	$ (89.9)
Adjustments to reconcile net loss to net cash from operating activities:
Depreciation and amortization	81.8	100.3
Charge for early retirement of debt	3.3	3.1
Deferred income taxes	(3.5)	(101.4)
Impairment of Long-Lived Assets Held-for-use	66.4	235.5
Loss on asset disposal	0.0	(49.2)
Gain (Loss) on Sale of Assets and Asset Impairment Charges	15.9	0.1
Changes in certain assets and liabilities:
Accounts receivable	15.8	23.6
Inventories	9.5	29.1
Prepaid taxes	0.0	0.2
Taxes applicable to subsequent years	61.4	61.5
Deferred regulatory costs, net	(6.5)	19.5
Accounts payable	(46.4)	(10.2)
Accrued taxes payable	(93.5)	(34.2)
Accrued interest payable	8.8	13.9
Security deposits	1.1	(0.6)
Increase (Decrease) in Obligation, Pension and Other Postretirement Benefits	3.8	(2.2)
Other	(6.9)	(0.5)
Net cash provided by operating activities	81.7	198.6
Cash flows from investing activities:
Capital expenditures	(95.6)	(109.8)
Proceeds from sale of business	0.0	75.5
Insurance proceeds	12.6	5.2
Purchase of intangible assets	(0.1)	(0.3)
Decrease in restricted cash	27.0	5.5
Other investing activities, net	0.3	0.8
Net cash used in investing activities	(55.8)	(23.1)
Cash flows from financing activities:
Payments of Deferred Finance Costs	0.0	(8.0)
Proceeds from Issuance of Long-term Debt	0.0	442.8
Proceeds from Lines of Credit	80.0	0.0
Retirement of long-term debt	(122.1)	(520.8)
Proceeds from (Payments for) Other Financing Activities	0.0	(0.1)
Net cash used in financing activities	(57.1)	(86.1)
Cash and cash equivalents:
Net change	(31.2)	89.4
Balance at beginning of period	54.6	32.4
Cash and cash equivalents at end of period	23.4	121.8
Supplemental cash flow information:
Interest paid, net of amounts capitalized	69.0	61.1
Proceeds from Income Tax Refunds	0.0	0.3
Non-cash financing and investing activities:
Accruals for capital expenditures	9.2	15.9
THE DAYTON POWER AND LIGHT COMPANY [Member]
Cash flows from operating activities:
Net income	3.6	(467.8)
Adjustments to reconcile net loss to net cash from operating activities:
Depreciation and amortization	68.2	95.2
Charge for early retirement of debt	1.1	0.5
Deferred income taxes	1.6	(314.2)
Impairment of Long-Lived Assets Held-for-use	66.3	857.1
Gain (Loss) on Sale of Assets and Asset Impairment Charges	15.9	0.2
Changes in certain assets and liabilities:
Accounts receivable	20.5	(11.0)
Inventories	10.0	29.4
Prepaid taxes	0.0	2.7
Taxes applicable to subsequent years	60.0	59.9
Deferred regulatory costs, net	(6.5)	19.5
Accounts payable	(58.4)	(13.5)
Accrued taxes payable	(83.9)	(43.2)
Accrued interest payable	(1.5)	(3.3)
Security deposits	1.1	(0.6)
Increase (Decrease) in Obligation, Pension and Other Postretirement Benefits	3.8	(2.2)
Other	(3.1)	11.7
Net cash provided by operating activities	98.7	220.4
Cash flows from investing activities:
Capital expenditures	(82.4)	(98.3)
Insurance proceeds	12.5	5.6
Purchase of intangible assets	(0.1)	(0.3)
Decrease in restricted cash	27.0	5.5
Other investing activities, net	0.3	0.9
Net cash used in investing activities	(42.7)	(86.6)
Cash flows from financing activities:
Payments of Deferred Finance Costs	0.0	(8.0)
Repayments of Lines of Credit	(15.0)	0.0
Proceeds from Issuance of Long-term Debt	0.0	442.8
Proceeds from Lines of Credit	30.0	0.0
Retirement of long-term debt	(103.3)	(445.3)
Payments of Ordinary Dividends, Common Stock	(19.0)	0.0
Issuance of short-term debt - related party	30.0	5.0
Repayment of short-term debt - related party	(35.0)	(40.0)
Proceeds from (Payments for) Other Financing Activities	0.0	(0.8)
Adjustments to Additional Paid in Capital, Dividends in Excess of Retained Earnings	(19.0)
Proceeds from Contributions from Parent	70.0	0.0
Net cash used in financing activities	(42.3)	(46.3)
Cash and cash equivalents:
Net change	13.7	87.5
Balance at beginning of period	1.6	5.4
Cash and cash equivalents at end of period	15.3	92.9
Supplemental cash flow information:
Interest paid, net of amounts capitalized	22.3	16.3
Non-cash financing and investing activities:
Accruals for capital expenditures	7.7	10.1
Subsidiary of Common Parent [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Non-cash financing and investing activities:
Equity Settlement of Related Party Payable	$ 0.0	$ 7.5