DPL (DPL) 10-Q 4 Nov 21 2021 Q3 Quarterly report Financial data

Cover Statement

Cover Statement	9 Months Ended
	Sep. 30, 2021shares
Entity Information [Line Items]
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q3
Entity Central Index Key	0000787250
Current Fiscal Year End Date	--12-31
Amendment Flag	false
Entity Current Reporting Status	Yes
Document Type	10-Q
Document Quarterly Report	true
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Shell Company	false
Document Period End Date	Sep. 30, 2021
Document Transition Report	false
Entity Registrant Name	DPL Inc.
Entity Incorporation, State or Country Code	OH
Entity File Number	1-9052
Entity Address, Address Line One	1065 Woodman Drive
Entity Address, City or Town	Dayton
Entity Address, State or Province	OH
Entity Address, Postal Zip Code	45432
City Area Code	937
Local Phone Number	259-7215
Entity Tax Identification Number	31-1163136
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding	1
Subsidiaries [Member]
Entity Information [Line Items]
Entity Central Index Key	0000027430
Amendment Flag	false
Entity Current Reporting Status	No
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Shell Company	false
Entity Registrant Name	THE DAYTON POWER AND LIGHT COMPANY
Entity Incorporation, State or Country Code	OH
Entity File Number	1-2385
Entity Address, Address Line One	1065 Woodman Drive
Entity Address, City or Town	Dayton
Entity Address, State or Province	OH
Entity Address, Postal Zip Code	45432
City Area Code	937
Local Phone Number	259-7215
Entity Tax Identification Number	31-0258470
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding	41,172,173

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Revenues	$ 188.2	$ 178.8	$ 511.5	$ 505.1
Operating costs and expenses
Net fuel cost	0	0.4	0.5	1.3
Utilities Operating Expense, Purchased Power	83.9	66	209.3	178
Operating expenses:
Operation and maintenance	40.1	48	112.9	138.8
Depreciation and amortization	18.9	18.6	56.9	54.8
Taxes other than income taxes	21	17.7	62.1	59.6
Costs and Expenses	163.9	150.7	441.7	432.5
Operating income	24.3	28.1	69.8	72.6
Other expense, net:
Interest expense	(15.8)	(17.1)	(47)	(55.4)
Gain (Loss) on Extinguishment of Debt	0	(31.7)	0	(31.7)
Other income / (expense)	(0.8)	1	0.3	0.9
Total other expense, net	(16.6)	(47.8)	(46.7)	(86.2)
Income / (loss) from continuing operations before income tax	7.7	(19.7)	23.1	(13.6)
Income tax benefit from continuing operations	(0.8)	(10.4)	(0.2)	(7.7)
Net income / (loss) from continuing operations	8.5	(9.3)	23.3	(5.9)
Income / (loss) from discontinued operations before income tax	0	1.4	(1)	(0.6)
Income tax expense / (benefit) from discontinued operations	0	0.3	(0.2)	0.8
Net income / (loss) from discontinued operations	0	1.1	(0.8)	3.1
Net income / (loss)	8.5	(8.2)	22.5	(2.8)
Subsidiaries [Member]
Revenues	186.1	177	504.8	499.1
Operating costs and expenses
Net fuel cost	0	0.4	0.5	1.3
Utilities Operating Expense, Purchased Power	83.7	65.7	208.5	177.1
Operating expenses:
Operation and maintenance	39.3	47.9	111.6	137.8
Depreciation and amortization	18.6	18.2	55.8	53.7
Taxes other than income taxes	21	17.8	62	59.6
Costs and Expenses	162.6	150	438.4	429.5
Operating income	23.5	27	66.4	69.6
Other expense, net:
Interest expense	(6.1)	(5.9)	(18.1)	(18.5)
Other income / (expense)	(1.3)	0.2	(1.6)	(1.4)
Total other expense, net	(7.4)	(5.7)	(19.7)	(19.9)
Income / (loss) from continuing operations before income tax	16.1	21.3	46.7	49.7
Income tax benefit from continuing operations	2.7	3.5	6.4	2.4
Net income / (loss)	$ 13.4	$ 17.8	$ 40.3	$ 47.3

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Net income	$ 8.5	$ (8.2)	$ 22.5	$ (2.8)
Derivative activity:
Change in derivative fair value, net of income tax	0	0.1	0	0
Reclassification of earnings, net of income tax	(0.2)	(0.3)	(0.6)	(0.8)
Total change in fair value of derivatives	(0.2)	(0.2)	(0.6)	(0.8)
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, Tax	0.1	0	0.4	(0.1)
Pension and postretirement activity:
Reclassification to earnings, net of income tax	0.5	0.3	1.5	0.8
Total change in unfunded pension obligation	0.5	0.3	1.5	0.8
Other comprehensive income	0.3	0.1	0.9	0
Net comprehensive income / (loss)	8.8	(8.1)	23.4	(2.8)
Subsidiaries [Member]
Net income	13.4	17.8	40.3	47.3
Derivative activity:
Change in derivative fair value, net of income tax	0	0.2	0	0.1
Reclassification of earnings, net of income tax	0	(0.1)	0	(0.3)
Total change in fair value of derivatives	0	0.1	0	(0.2)
Pension and postretirement activity:
Reclassification to earnings, net of income tax	1	0.8	2.9	2.4
Total change in unfunded pension obligation	1	0.8	2.9	2.4
Other comprehensive income	1	0.9	2.9	2.2
Net comprehensive income / (loss)	$ 14.4	$ 18.7	$ 43.2	$ 49.5

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Comprehensive Income (Parenthetical) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Income tax (expense)/benefit on unrealized gains (losses) related to derivative activity	$ 0	$ 0	$ 0	$ 0
Income tax (expense)/benefit on reclassification of earnings related to derivative activity	0	0	0.1	0.1
Subsidiaries [Member]
Income tax (expense)/benefit on unrealized gains (losses) related to derivative activity	0	0	0	0
Income tax (expense)/benefit on reclassification of earnings related to derivative activity	0	(0.1)	0	(0.1)
Income tax (expense)/benefit on reclassification of earnings related to pension and postretirement activity	$ (0.3)	$ (0.2)	$ (0.9)	$ (0.6)

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 41.5	$ 25.4
Restricted cash	0.1	0.1
Accounts receivable, net	68.3	69.7
Accounts Receivable, Allowance for Credit Loss, Current	0.9	2.8
Inventories	12.4	8.8
Taxes applicable to subsequent years	19.4	78
Regulatory assets, current	24.5	27.5
Income Taxes Receivable, Current	18.4	17.9
Prepayments and other current assets	10.1	5.8
Total current assets	194.7	233.2
Property, plant & equipment:
Property, plant & equipment	1,952.4	1,839.3
Less: Accumulated depreciation and amortization	(455.2)	(415.7)
Property, plant and equipment, net of depreciation	1,497.2	1,423.6
Construction work in process	153.3	141.7
Total net property, plant & equipment	1,650.5	1,565.3
Other non-current assets:
Regulatory assets, non-current	191.7	193.6
Intangible assets, net of amortization	21.9	19.3
Other non-current assets	29.9	24.6
Total other non-current assets	243.5	237.5
Total assets	2,088.7	2,036
Current liabilities:
Current portion of long-term debt	220.2	100.2
Accounts payable	76.5	84.5
Accrued taxes	86	83
Accrued interest	18.4	16
Security deposits	17.8	19.4
Regulatory liabilities, current	18.9	18
Other current liabilities	19.8	21
Total current liabilities	457.6	342.1
Non-current liabilities:
Long-term debt	1,394.9	1,393.4
Deferred taxes	184.9	177.2
Taxes payable	2.4	80.4
Regulatory liabilities, non-current	214.8	218.3
Pension, retiree and other benefits	81.7	93.9
Other deferred credits	12.5	14.2
Total non-current liabilities	1,891.2	1,977.4
Commitments and contingencies
Common shareholder's equity:
Common stock	0	0
Other paid-in capital	2,468.8	2,468.8
Accumulated other comprehensive income	(11.4)	(12.3)
Retained Earnings (Accumulated Deficit)	(2,717.5)	(2,740)
Total common shareholder's equity	(260.1)	(283.5)
Total liabilities and shareholder's equity	$ 2,088.7	$ 2,036
Common Stock, Shares Authorized	1,500	1,500
Common stock, shares issued	1	1
Common Stock [Member]
Common shareholder's equity:
Total common shareholder's equity	$ 0	$ 0
Other Additional Capital [Member]
Common shareholder's equity:
Total common shareholder's equity	2,468.8	2,468.8
Subsidiaries [Member]
Current assets:
Cash and cash equivalents	29.8	11.7
Restricted cash	0.1	0.1
Accounts receivable, net	68.5	70.2
Accounts Receivable, Allowance for Credit Loss, Current	0.9	2.8
Inventories	12.4	8.8
Taxes applicable to subsequent years	19.4	77.6
Regulatory assets, current	24.5	27.5
Income Taxes Receivable, Current	30.3	32.5
Prepayments and other current assets	11.4	6.4
Total current assets	196.4	234.8
Property, plant & equipment:
Property, plant & equipment	2,535.8	2,437.3
Less: Accumulated depreciation and amortization	(1,056.4)	(1,032.1)
Property, plant and equipment, net of depreciation	1,479.4	1,405.2
Construction work in process	149.6	138.8
Total net property, plant & equipment	1,629	1,544
Other non-current assets:
Regulatory assets, non-current	191.7	193.6
Intangible assets, net of amortization	20.8	18.3
Other non-current assets	29.7	24
Total other non-current assets	242.2	235.9
Total assets	2,067.6	2,014.7
Current liabilities:
Current portion of long-term debt	140.2	20.2
Accounts payable	76.3	85.5
Accrued taxes	87.3	82.7
Accrued interest	6	2.6
Security deposits	17.6	19.1
Regulatory liabilities, current	18.9	18
Other current liabilities	14.9	25
Total current liabilities	361.2	253.1
Non-current liabilities:
Long-term debt	574	573.9
Deferred taxes	184.5	172.1
Taxes payable	2.4	80.3
Regulatory liabilities, non-current	214.8	218.3
Pension, retiree and other benefits	81.7	93.9
Other deferred credits	6	6.4
Total non-current liabilities	1,063.4	1,144.9
Commitments and contingencies
Par value common shares (in USD per share)	$ 0.01	$ 0.01
Common shareholder's equity:
Common stock	$ 0.4	$ 0.4
Other paid-in capital	697.5	714.4
Accumulated other comprehensive income	(39.2)	(42.1)
Retained Earnings (Accumulated Deficit)	(15.7)	(56)
Total common shareholder's equity	643	616.7
Total liabilities and shareholder's equity	$ 2,067.6	$ 2,014.7
Common Stock, Shares, Outstanding	41,172,173	41,172,173
Common Stock, Shares Authorized	50,000,000	50,000,000
Subsidiaries [Member] | Common Stock [Member]
Common shareholder's equity:
Total common shareholder's equity	$ 0.4
Subsidiaries [Member] | Other Additional Capital [Member]
Common shareholder's equity:
Total common shareholder's equity	$ 697.5

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2021	Dec. 31, 2020
Common Stock, Shares Authorized	1,500	1,500
Common stock, shares issued	1	1
Subsidiaries [Member]
Common Stock, Shares Authorized	50,000,000	50,000,000
Common Stock, Shares, Outstanding	41,172,173	41,172,173
Common stock, par value (in USD per share)	$ 0.01	$ 0.01

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Cash flows from operating activities:
Net income	$ 22.5	$ (2.8)
Adjustments to reconcile net income / (loss) to net cash from operating activities:
Deferred income taxes	2.3	32.3
Depreciation and amortization	56.9	55.1
Gain (Loss) on Disposition of Business, Including Discontinued Operation	0	(4.5)
Changes in certain assets and liabilities:
Accounts receivable, net	1.5	12.7
Inventories	(3.6)	5.5
Taxes applicable to subsequent years	58.6	57.8
Deferred regulatory costs, net	5.1	(17.1)
Prepayments and other current assets	(4.4)	2.5
Increase (Decrease) in Other Noncurrent Assets	(4.8)	2.7
Accounts payable	7.1	(24.6)
Accrued taxes payable / receivable	(75.5)	(63)
Accrued interest	2.4	7.4
Increase (Decrease) in Other Accrued Liabilities	(1.6)	(4.5)
Increase (Decrease) in Obligation, Pension and Other Postretirement Benefits	(12.2)	(10.8)
Other	2.2	1.3
Net Cash Provided by (Used in) Operating Activities	56.5	81.7
Cash flows from investing activities:
Capital expenditures	(144.5)	(107.5)
Payments for (Proceeds from) Removal Costs	(13.8)	(21.2)
Payments for Removal Costs	(1.2)	(1)
Proceeds from Sale of Productive Assets	0	5.1
Other investing activities, net	(0.7)	(0.8)
Net cash used in investing activities	(160.2)	(125.4)
Cash flows from financing activities:
Proceeds from (Payments for) Other Financing Activities	0	(0.1)
Proceeds from Contributions from Parent	0	98
Payments of Deferred Finance Costs	(0.2)	(7.8)
Repayments of Lines of Credit	0	(219)
Proceeds from Issuance of Long-term Debt	0	555
Retirement of long-term debt	0	(550.8)
Proceeds from Lines of Credit	120	165
Net cash provided by financing activities	119.8	40.3
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	16.1	(3.4)
Cash, cash equivalents, and restricted cash:
Restricted Cash and Cash Equivalents	41.6	43.6
Non-cash financing and investing activities:
Accruals for capital expenditures	15.1	16.5
Non-cash Proceeds from Sale of Business	0	3
Supplemental cash flow information:
Interest paid, net of amounts capitalized	41.5	49.7
Income Taxes Paid, Net	0	(51.9)
Gain (Loss) on Extinguishment of Debt	0	31.7
Subsidiaries [Member]
Cash flows from operating activities:
Net income	40.3	47.3
Adjustments to reconcile net income / (loss) to net cash from operating activities:
Deferred income taxes	6.4	(0.1)
Depreciation and amortization	55.8	53.7
Changes in certain assets and liabilities:
Accounts receivable, net	1.6	1.7
Inventories	(3.6)	2.1
Taxes applicable to subsequent years	58.3	57.7
Deferred regulatory costs, net	5.1	(17.1)
Prepayments and other current assets	(5.2)	4.1
Increase (Decrease) in Other Noncurrent Assets	(5.7)	1
Accounts payable	6	(20.6)
Accrued taxes payable / receivable	(71)	(71.6)
Accrued interest	3.3	4.6
Increase (Decrease) in Other Accrued Liabilities	(1.5)	(4.8)
Increase (Decrease) in Obligation, Pension and Other Postretirement Benefits	(12.2)	(10.8)
Other	3.7	2.5
Net Cash Provided by (Used in) Operating Activities	81.3	49.7
Cash flows from investing activities:
Capital expenditures	(143.3)	(103.9)
Payments for (Proceeds from) Removal Costs	(13.8)	(21.2)
Other investing activities, net	0.9	(0.7)
Net cash used in investing activities	(156.2)	(125.8)
Cash flows from financing activities:
Payments of Ordinary Dividends, Common Stock	(27)	(27.7)
Proceeds from (Payments for) Other Financing Activities	0	(0.1)
Proceeds from Contributions from Parent	0	150
Payments of Deferred Finance Costs	0	(1.2)
Repayments of Lines of Credit	0	(115)
Proceeds from Issuance of Long-term Debt	0	140
Retirement of long-term debt	0	(140)
Proceeds from Lines of Credit	120	75
Net cash provided by financing activities	93	81
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	18.1	4.9
Cash, cash equivalents, and restricted cash:
Restricted Cash and Cash Equivalents	29.9	26.2
Non-cash financing and investing activities:
Accruals for capital expenditures	15.1	16.4
Supplemental cash flow information:
Interest paid, net of amounts capitalized	12.6	10.5
Proceeds from Income Tax Refunds	$ 0	$ 0.1

Statement of Equity Statement

Statement of Equity Statement - USD ($) $ in Millions	Total	Common Stock [Member]	Other Additional Capital [Member]	AOCI Attributable to Parent [Member]	Retained Earnings [Member]	Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member]	Subsidiaries [Member]	Subsidiaries [Member]Common Stock [Member]	Subsidiaries [Member]Other Additional Capital [Member]	Subsidiaries [Member]AOCI Attributable to Parent [Member]	Subsidiaries [Member]Retained Earnings [Member]
Shares, Issued		1						41,172,173
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Beginning Balance at Dec. 31, 2019	$ (371.9)	$ 0	$ 2,370.7	$ (3.6)	$ (2,739)		$ 473.4	$ 0.4	$ 617	$ (36.9)	$ (107.1)
Other Comprehensive Income (Loss), Net of Tax	(0.3)						0.4
Net income/ (loss)	1.9
Net Income (Loss) Attributable to Parent							11.7
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	1.6						12.1
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Ending Balance at Mar. 31, 2020	(370.3)	0	2,370.7	(3.9)	(2,737.1)		485.5	0.4	617	(36.5)	(95.4)
Dividends, Common Stock, Cash							(42.7)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Beginning Balance at Dec. 31, 2019	(371.9)	0	2,370.7	(3.6)	(2,739)		473.4	0.4	617	(36.9)	(107.1)
Other Comprehensive Income (Loss), Net of Tax	0						2.2
Net income/ (loss)	(2.8)						47.3
Proceeds from Contributions from Parent	(98)						(150)
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	(2.8)						49.5
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Ending Balance at Sep. 30, 2020	(276.6)	$ 0	2,468.8	(3.6)	(2,741.8)		630.3	$ 0.4	724.4	(34.7)	(59.8)
Shares, Issued		1						41,172,173
Dividends, Common Stock, Cash							(14.2)		(14.2)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Beginning Balance at Mar. 31, 2020	(370.3)	$ 0	2,370.7	(3.9)	(2,737.1)		485.5	$ 0.4	617	(36.5)	(95.4)
Other Comprehensive Income (Loss), Net of Tax				0.2			0.9
Net Income (Loss) Attributable to Parent					3.5		17.8
Proceeds from Contributions from Parent							(150)		(150)
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	3.7						18.7
Non-cash capital contribution	98		98
Stockholders' Equity, Other							(0.1)		(0.1)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Ending Balance at Jun. 30, 2020	(268.6)	$ 0	2,468.7	(3.7)	(2,733.6)		640.1	$ 0.4	752.9	(35.6)	(77.6)
Shares, Issued		1						41,172,173
Dividends, Common Stock, Cash							(28.5)		(28.5)
Other Comprehensive Income (Loss), Net of Tax	0.1			0.1			0.9
Net income/ (loss)	(8.2)						17.8
Net Income (Loss) Attributable to Parent					(8.2)		17.8
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	(8.1)						18.7
Stockholders' Equity, Other	0.1		(0.1)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Ending Balance at Sep. 30, 2020	$ (276.6)	$ 0	2,468.8	(3.6)	(2,741.8)		$ 630.3	$ 0.4	724.4	(34.7)	(59.8)
Shares, Issued		1						41,172,173
Common stock, par value (in USD per share)							$ 0.01
Common Stock, Shares Authorized	1,500						50,000,000
Shares, Issued		1						41,172,173
Common Stock, Value, Issued	$ 0						$ 0.4
Additional Paid in Capital, Common Stock	2,468.8						714.4
Accumulated Other Comprehensive Income (Loss), Net of Tax	(12.3)					$ 13.6	(42.1)
Retained Earnings (Accumulated Deficit)	(2,740)						(56)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Beginning Balance at Dec. 31, 2020	(283.5)	$ 0	2,468.8	(12.3)	(2,740)		616.7
Other Comprehensive Income (Loss), Net of Tax	0.3									1
Net income/ (loss)	13.6
Net Income (Loss) Attributable to Parent											18.3
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	13.9						19.3
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Ending Balance at Mar. 31, 2021	(269.6)	0	2,468.8	(12)	(2,726.4)		636	$ 0.4	714.4	(41.1)	(37.7)
Dividends, Common Stock, Cash									(17)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Beginning Balance at Dec. 31, 2020	(283.5)	0	2,468.8	(12.3)	(2,740)		616.7
Other Comprehensive Income (Loss), Net of Tax	0.9					(0.6)	2.9
Net income/ (loss)	22.5						40.3
Proceeds from Contributions from Parent	0						0
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	23.4						43.2
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Ending Balance at Sep. 30, 2021	(260.1)	$ 0	2,468.8	(11.4)	(2,717.5)		643	$ 0.4	697.5	(39.2)	(15.7)
Shares, Issued		1						41,172,173
Dividends, Common Stock, Cash							(7)		(7)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Beginning Balance at Mar. 31, 2021	(269.6)	$ 0	2,468.8	(12)	(2,726.4)		636	$ 0.4	714.4	(41.1)	(37.7)
Other Comprehensive Income (Loss), Net of Tax	0.3									0.9
Net Income (Loss) Attributable to Parent					0.4						8.6
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	0.7						9.5
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Ending Balance at Jun. 30, 2021	(268.9)	$ 0	2,468.8	(11.7)	(2,726)		638.5	$ 0.4	707.4	(40.2)	(29.1)
Shares, Issued		1						41,172,173
Dividends, Common Stock, Cash							(10)		(10)
Other Comprehensive Income (Loss), Net of Tax	0.3						1			1
Net income/ (loss)	8.5						13.4
Net Income (Loss) Attributable to Parent					8.5						13.4
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	8.8						14.4
Stockholders' Equity, Other							0.1		0.1
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Ending Balance at Sep. 30, 2021	$ (260.1)	$ 0	$ 2,468.8	$ (11.4)	$ (2,717.5)		$ 643	$ 0.4	$ 697.5	$ (39.2)	$ (15.7)
Common stock, par value (in USD per share)							$ 0.01
Common Stock, Shares Authorized	1,500						50,000,000
Shares, Issued		1						41,172,173
Common Stock, Value, Issued	$ 0						$ 0.4
Additional Paid in Capital, Common Stock	2,468.8						697.5
Accumulated Other Comprehensive Income (Loss), Net of Tax	(11.4)					$ 13	(39.2)
Retained Earnings (Accumulated Deficit)	$ (2,717.5)						$ (15.7)

Overview and Summary of Signifi

Overview and Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2021
Significant Accounting Policies [Line Items]
Overview and Summary of Significant Accounting Policies	Overview and Summary of Significant Accounting Policies Description of Business DPL is a regional energy company organized in 1985 under the laws of Ohio. DPL has one reportable segment, the Utility segment. See Note 10 – Business Segments for more information relating to this reportable segment. The terms “we,” “us,” “our” and “ours” are used to refer to DPL and its subsidiaries. DPL is an indirectly wholly-owned subsidiary of AES. DP&L , a wholly-owned subsidiary of DPL that does business as AES Ohio , is a public utility incorporated in 1911 under the laws of Ohio. Beginning in 2001, Ohio law gave Ohio consumers the right to choose the electric generation supplier from whom they purchase retail generation service; however, retail transmission and distribution services are still regulated. AES Ohio has the exclusive right to provide such transmission and distribution services to approximately 533,000 customers located in West Central Ohio. Additionally, AES Ohio provides retail SSO electric service to residential, commercial, industrial and governmental customers in a 6,000-square mile area of West Central Ohio. AES Ohio sources all of the generation for its SSO customers through a competitive bid process. Principal industries located in AES Ohio’s service territory include automotive, food processing, paper, plastic, manufacturing and defense. AES Ohio's sales reflect the general economic conditions, seasonal weather patterns of the area, the market price of electricity and customer energy efficiency initiatives. AES Ohio owned interests in the retired Hutchings Coal Station until its transfer in 2020 and currently owns numerous transmission facilities. AES Ohio sells its proportional share of energy and capacity from its investment in OVEC into the wholesale market. DPL’s other primary subsidiaries are MVIC and Miami Valley Lighting. MVIC is our captive insurance company that provides insurance services to AES Ohio and our other subsidiaries, and Miami Valley Lighting provides street and outdoor lighting services to customers in the Dayton region. In prior periods, AES Ohio Generation was also a primary subsidiary and sold all of its energy and capacity into the wholesale market. AES Ohio Generation retired its only remaining operating asset in May 2020 and sold it in June 2020. See Note 12 – Discontinued Operations for more information. DPL's subsidiaries are all wholly-owned. DPL also has a wholly-owned business trust, DPL Capital Trust II, formed for the purpose of issuing trust capital securities to investors. AES Ohio’s electric transmission and distribution businesses are subject to rate regulation by federal and state regulators. Accordingly, AES Ohio applies the accounting standards for regulated operations to its electric transmission and distribution businesses and records regulatory assets when incurred costs are expected to be recovered in future customer rates and regulatory liabilities when current cost recoveries in customer rates relate to expected future costs or overcollections of riders. Financial Statement Presentation DPL’s Condensed Consolidated Financial Statements include the accounts of DPL and its wholly-owned subsidiaries except for DPL Capital Trust II, which is not consolidated, consistent with the provisions of GAAP. Certain immaterial amounts from prior periods have been reclassified to conform to the current period presentation. All material intercompany accounts and transactions are eliminated in consolidation. We have evaluated subsequent events through the date this report is issued. These financial statements have been prepared in accordance with GAAP, as contained in the FASB ASC, for interim financial statements and Article 10 of Regulation S-X issued by the SEC. Accordingly, they do not include all the information and footnotes required by GAAP for annual fiscal reporting periods. Therefore, our interim financial statements in this report should be read along with the annual financial statements included in our Form 10-K for the fiscal year ended December 31, 2020. In the opinion of our management, the Condensed Consolidated Financial Statements presented in this report contain all adjustments necessary to fairly state our financial position as of September 30, 2021; our results of operations for the three and nine months ended September 30, 2021 and 2020, our cash flows for the nine months ended September 30, 2021 and 2020 and the changes in our equity for the three and nine months ended September 30, 2021 and 2020. Unless otherwise noted, all adjustments are normal and recurring in nature. Due to various factors, interim results for the three and nine months ended September 30, 2021 may not be indicative of our results that will be realized for the full year ending December 31, 2021. The preparation of financial statements in conformity with GAAP requires us to make estimates and judgments that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities, and the revenues and expenses of the periods reported. Actual results could differ from these estimates. Significant items subject to such estimates and judgments include: recognition of revenue including unbilled revenues, the carrying value of property, plant and equipment; the valuation of insurance and claims liabilities; the valuation of allowances for credit losses and deferred income taxes; regulatory assets and liabilities; liabilities recorded for income tax exposures; litigation; contingencies; and assets and liabilities related to employee benefits. Cash, Cash Equivalents and Restricted Cash The following table provides a summary of cash, cash equivalents, and restricted cash amounts reported on the Condensed Consolidated Balance Sheets that reconcile to the total of such amounts as shown on the Condensed Consolidated Statements of Cash Flows: $ in millions September 30, 2021 December 31, 2020 Cash and cash equivalents $ 41.5 $ 25.4 Restricted cash 0.1 0.1 Cash, Cash Equivalents, and Restricted Cash, End of Period $ 41.6 $ 25.5 Accounts Receivable and Allowance for Credit Losses Accounts receivable were as follows as of September 30, 2021 and December 31, 2020: September 30, December 31, $ in millions 2021 2020 Accounts receivable, net: Customer receivables $ 47.3 $ 48.5 Unbilled revenue 15.6 21.6 Amounts due from affiliates 1.5 0.2 Due from PJM transmission enhancement settlement 1.7 1.7 Other 3.1 0.5 Allowance for credit losses (0.9) (2.8) Total accounts receivable, net $ 68.3 $ 69.7 The following table is a roll forward of our allowance for credit losses related to the accounts receivable balances for the nine months ended September 30, 2021 and 2020: $ in millions Beginning Allowance Balance Current Period Provision Write-offs Charged Against Allowances Recoveries Collected Ending Allowance Balance 2021 $ 2.8 $ (0.4) $ (2.6) $ 1.1 $ 0.9 2020 $ 0.4 $ 2.8 $ (1.4) $ 1.4 $ 3.2 The allowance for credit losses primarily relates to utility customer receivables, including unbilled amounts. Expected credit loss estimates are developed by disaggregating customers into those with similar credit risk characteristics and using historical credit loss experience. In addition, we also consider how current and future economic conditions are expected to impact collectability, as applicable, including the economic impacts of the COVID-19 pandemic on our receivable balance as of September 30, 2021. Amounts are written off when reasonable collections efforts have been exhausted. During 2021, the current period provision and allowance for credit losses have decreased due to lower past due customer receivable balances. See Note 13 – Risks and Uncertainties for additional discussion of the COVID-19 pandemic. Inventories Inventories consist of materials and supplies as of September 30, 2021 and December 31, 2020. Accounting for Taxes Collected from Customers and Remitted to Governmental Authorities AES Ohio collects certain excise taxes levied by state or local governments from its customers. These taxes are accounted for on a net basis and not included in revenue. The amounts of such taxes collected for the three and nine months ended September 30, 2021 and 2020 were as follows: Three months ended Nine months ended September 30, September 30, $ in millions 2021 2020 2021 2020 Excise taxes collected $ 13.5 $ 13.4 $ 37.7 $ 36.7 Accumulated other comprehensive loss The amounts reclassified out of Accumulated other comprehensive loss by component during the three and nine months ended September 30, 2021 and 2020 are as follows: Details about Accumulated Other Comprehensive Loss components Affected line item in the Condensed Consolidated Statements of Operations Three months ended Nine months ended September 30, September 30, $ in millions 2021 2020 2021 2020 Gains and losses on cash flow hedges (Note 4): Interest expense $ (0.2) $ (0.3) $ (0.7) $ (0.9) Income tax expense — — 0.1 0.1 Net of income taxes (0.2) (0.3) (0.6) (0.8) Amortization of defined benefit pension items (Note 7): Other expense 0.6 0.3 1.9 0.9 Income tax benefit (0.1) — (0.4) (0.1) Net of income taxes 0.5 0.3 1.5 0.8 Total reclassifications for the period, net of income taxes $ 0.3 $ — $ 0.9 $ — The changes in the components of Accumulated other comprehensive loss during the nine months ended September 30, 2021 are as follows: $ in millions Gains / (losses) on cash flow hedges Change in unfunded pension and postretirement benefit obligations Total Balance as of January 1, 2021 $ 13.6 $ (25.9) $ (12.3) Amounts reclassified from AOCL to earnings (0.6) 1.5 0.9 Net current period other comprehensive income / (loss) (0.6) 1.5 0.9 Balance as of September 30, 2021 $ 13.0 $ (24.4) $ (11.4) New Accounting Pronouncements Adopted in 2021 – We have assessed and determined that the new accounting pronouncements adopted did not have a material impact on our consolidated financial statements. New Accounting Pronouncements Issued But Not Yet Effective – The following table provides a brief description of recent accounting pronouncements that could have a material impact on our consolidated financial statements. Accounting pronouncements not listed below were assessed and determined to be either not applicable or are expected to have no material impact on our consolidated financial statements. ASU Number and Name Description Date of Adoption Effect on the financial statements upon adoption 2020-04, Reference Rate Form (Topic 848): Facilitation of the Effects of Reference Rate Reform on Financial Reporting The standard provides optional expedients and exceptions for applying GAAP to contracts, hedging relationships and other transactions that reference to LIBOR or another reference rate expected to be discontinued by reference rate reform. This standard is effective for a limited period of time (March 12, 2020 - December 21, 2022). Effective for all entities March 12, 2020 - December 31, 2022 We are currently evaluating the impact of adopting the standard on our condensed consolidated financial statements.
Subsidiaries [Member]
Significant Accounting Policies [Line Items]
Overview and Summary of Significant Accounting Policies	Overview and Summary of Significant Accounting Policies Description of Business DP&L , which does business as AES Ohio , is a public utility incorporated in 1911 under the laws of Ohio. Beginning in 2001, Ohio law gave Ohio consumers the right to choose the electric generation supplier from whom they purchase retail generation service; however, retail transmission and distribution services are still regulated. AES Ohio has the exclusive right to provide such transmission and distribution services to approximately 533,000 customers located in West Central Ohio. Additionally, AES Ohio provides retail SSO electric service to residential, commercial, industrial and governmental customers in a 6,000-square mile area of West Central Ohio. AES Ohio sources all of the generation for its SSO customers through a competitive bid process. Principal industries located in AES Ohio’s service territory include automotive, food processing, paper, plastic, manufacturing and defense. AES Ohio's sales reflect the general economic conditions, seasonal weather patterns of the area, the market price of electricity and customer energy efficiency initiatives. AES Ohio owned interests in the retired Hutchings Coal Station until its transfer in 2020 and currently owns numerous transmission facilities. AES Ohio sells its proportional share of energy and capacity from its investment in OVEC into the wholesale market. AES Ohio has one reportable segment, the Utility segment. In addition to AES Ohio's electric transmission and distribution businesses, the Utility segment includes revenues and costs associated with AES Ohio's investment in OVEC and the historical results of AES Ohio’s Hutchings Coal Station. AES Ohio is a subsidiary of DPL. The terms “we,” “us,” “our” and “ours” are used to refer to AES Ohio . AES Ohio’s electric transmission and distribution businesses are subject to rate regulation by federal and state regulators. Accordingly, AES Ohio applies the accounting standards for regulated operations to its electric transmission and distribution businesses and records regulatory assets when incurred costs are expected to be recovered in future customer rates and regulatory liabilities when current cost recoveries in customer rates relate to expected future costs or overcollections of riders. Financial Statement Presentation AES Ohio does not have any subsidiaries. We have evaluated subsequent events through the date this report is issued. Certain immaterial amounts from prior periods have been reclassified to conform to the current period presentation. These financial statements have been prepared in accordance with GAAP, as contained in the FASB ASC, for interim financial statements and Article 10 of Regulation S-X issued by the SEC. Accordingly, they do not include all the information and footnotes required by GAAP for annual fiscal reporting periods. Therefore, our interim financial statements in this report should be read along with the annual financial statements included in our Form 10-K for the fiscal year ended December 31, 2020. In the opinion of our management, the Condensed Financial Statements presented in this report contain all adjustments necessary to fairly state our financial position as of September 30, 2021; our results of operations for the three and nine months ended September 30, 2021 and 2020, our cash flows for the nine months ended September 30, 2021 and 2020 and the changes in our equity for the three and nine months ended September 30, 2021 and 2020. Unless otherwise noted, all adjustments are normal and recurring in nature. Due to various factors, interim results for the three and nine months ended September 30, 2021 may not be indicative of our results that will be realized for the full year ending December 31, 2021. The preparation of financial statements in conformity with GAAP requires us to make estimates and judgments that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities, and the revenues and expenses of the periods reported. Actual results could differ from these estimates. Significant items subject to such estimates and judgments include: recognition of revenue including unbilled revenues, the carrying value of property, plant and equipment; the valuation of insurance and claims liabilities; the valuation of allowances for credit losses and deferred income taxes; regulatory assets and liabilities; liabilities recorded for income tax exposures; litigation; contingencies; and assets and liabilities related to employee benefits. Cash, Cash Equivalents and Restricted Cash The following table provides a summary of cash, cash equivalents, and restricted cash amounts reported on the Condensed Balance Sheets that reconcile to the total of such amounts as shown on the Condensed Statements of Cash Flows: $ in millions September 30, 2021 December 31, 2020 Cash and cash equivalents $ 29.8 $ 11.7 Restricted cash 0.1 0.1 Cash, Cash Equivalents, and Restricted Cash, End of Period $ 29.9 $ 11.8 Accounts Receivable and Allowance for Credit Losses Accounts receivable were as follows as of September 30, 2021 and December 31, 2020: September 30, December 31, $ in millions 2021 2020 Accounts receivable, net: Customer receivables 46.6 $ 47.6 Unbilled revenue 15.6 21.6 Amounts due from affiliates 2.3 1.9 Due from PJM transmission enhancement settlement 1.7 1.7 Other 3.2 0.2 Allowance for credit losses (0.9) (2.8) Total accounts receivable, net $ 68.5 $ 70.2 The following table is a roll forward of our allowance for credit losses related to the accounts receivable balances for the nine months ended September 30, 2021 and 2020: $ in millions Beginning Allowance Balance Current Period Provision Write-offs Charged Against Allowances Recoveries Collected Ending Allowance Balance 2021 $ 2.8 $ (0.4) $ (2.6) $ 1.1 $ 0.9 2020 $ 0.4 $ 2.8 $ (1.4) $ 1.4 $ 3.2 The allowance for credit losses primarily relates to utility customer receivables, including unbilled amounts. Expected credit loss estimates are developed by disaggregating customers into those with similar credit risk characteristics and using historical credit loss experience. In addition, we also consider how current and future economic conditions are expected to impact collectability, as applicable, including the economic impacts of the COVID-19 pandemic on our receivable balance as of September 30, 2021. Amounts are written off when reasonable collections efforts have been exhausted. During 2021, the current period provision and allowance for credit losses have decreased due to lower past due customer receivable balances. See Note 11 – Risks and Uncertainties for additional discussion of the COVID-19 pandemic. Inventories Inventories consist of materials and supplies as of September 30, 2021 and December 31, 2020. Accounting for Taxes Collected from Customers and Remitted to Governmental Authorities AES Ohio collects certain excise taxes levied by state or local governments from its customers. These taxes are accounted for on a net basis and not included in revenue. The amounts of such taxes collected for the three and nine months ended September 30, 2021 and 2020 were as follows: Three months ended Nine months ended September 30, September 30, $ in millions 2021 2020 2021 2020 Excise taxes collected $ 13.5 $ 13.4 $ 37.7 $ 36.7 Accumulated other comprehensive loss The amounts reclassified out of Accumulated other comprehensive loss by component during the three and nine months ended September 30, 2021 and 2020 are as follows: Details about Accumulated Other Comprehensive Loss components Affected line item in the Condensed Consolidated Statements of Operations Three months ended Nine months ended September 30, September 30, $ in millions 2021 2020 2021 2020 Gains and losses on cash flow hedges (Note 4): Interest expense $ — $ — $ — $ (0.2) Income tax benefit — (0.1) — (0.1) Net of income taxes — (0.1) — (0.3) Amortization of defined benefit pension items (Note 7): Other expense 1.3 1.0 3.8 3.0 Income tax benefit (0.3) (0.2) (0.9) (0.6) Net of income taxes 1.0 0.8 2.9 2.4 Total reclassifications for the period, net of income taxes $ 1.0 $ 0.7 $ 2.9 $ 2.1 The changes in the components of Accumulated other comprehensive loss during the nine months ended September 30, 2021 are as follows: $ in millions Change in Accumulated other comprehensive loss Balance as of January 1, 2021 $ (42.1) Amounts reclassified from AOCL to earnings 2.9 Net current period other comprehensive income 2.9 Balance as of September 30, 2021 $ (39.2) New Accounting Pronouncements Adopted in 2021 – We have assessed and determined that the new accounting pronouncements adopted did not have a material impact on our financial statements. New Accounting Pronouncements Issued But Not Yet Effective – The following table provides a brief description of recent accounting pronouncements that could have a material impact on our financial statements. Accounting pronouncements not listed below were assessed and determined to be either not applicable or are expected to have no material impact on our financial statements. ASU Number and Name Description Date of Adoption Effect on the financial statements upon adoption 2020-04, Reference Rate Form (Topic 848): Facilitation of the Effects of Reference Rate Reform on Financial Reporting The standard provides optional expedients and exceptions for applying GAAP to contracts, hedging relationships and other transactions that reference to LIBOR or another reference rate expected to be discontinued by reference rate reform. This standard is effective for a limited period of time (March 12, 2020 - December 21, 2022). Effective for all entities March 12, 2020 - December 31, 2022 We are currently evaluating the impact of adopting the standard on our condensed financial statements.

Regulatory Matters (Notes)

Regulatory Matters (Notes)	9 Months Ended
	Sep. 30, 2021
Schedule of Regulatory Assets and Liabilities [Text Block]	Regulatory Matters Smart Grid and Comprehensive Settlement On October 23, 2020, AES Ohio entered into a Stipulation and Recommendation (settlement) with the staff of the PUCO and various customers, and organizations representing customers of AES Ohio and certain other parties with respect to, among other matters, AES Ohio's applications pending at the PUCO for (i) approval of AES Ohio's plan to modernize its distribution grid (the Smart Grid Plan), (ii) findings that AES Ohio passed the SEET for 2018 and 2019, and (iii) findings that AES Ohio's current ESP 1 satisfies the SEET and the more favorable in the aggregate (MFA) regulatory test. A hearing was held in January 2021 for consideration of this settlement and on June 16, 2021, the PUCO issued their opinion and order accepting the stipulation as filed. Applications for rehearing of the PUCO's orders relating to the comprehensive settlement were filed on July 16, 2021 and remain pending. Consistent with AES’ earlier statement of intent and based on recent discussions with AES, with the PUCO’s issuance of their opinion and order, DPL and AES Ohio expect that AES will make cash contributions of $150.0 million in 2021 to enable Smart Grid investment. Decoupling On January 23, 2020 AES Ohio filed with the PUCO requesting approval to defer its decoupling costs consistent with the methodology approved in its Distribution Rate Case. If approved, deferral would be effective December 18, 2019 and going forward would reduce impacts of weather, energy efficiency programs and economic changes in customer demand. An evidentiary hearing was held on this matter on May 4, 2021. Distribution Rate Case On November 30, 2020, AES Ohio filed a new Distribution Rate Case with the PUCO. This rate case proposes a revenue increase of $120.8 million per year and incorporates the DIR investments that were planned and approved in the last rate case but not yet included in distribution rates, other distribution investments since September 2015 and investments necessitated by the tornados that occurred on Memorial Day in 2019. The rate case also includes a proposal for increased tree-trimming expenses and certain customer demand-side management programs and recovery of prior-approved regulatory assets for tree trimming, uncollectible expenses and rate case expense. This case is pending a commission order. On July 26, 2021, the PUCO staff filed its Staff Report of Investigation in the distribution rate case. Settlement negotiations are currently ongoing, and the hearing is set to begin on December 7, 2021. FERC Proceedings On March 3, 2020, AES Ohio filed an application before the FERC to change its transmission rate from a stated rate to a formula rate, which was accepted by the FERC and made effective as of May 3, 2020, subject to further proceedings and potential refunds. An uncontested settlement was filed December 10, 2020 and approved April 15, 2021. Among other things, the settlement established new depreciation rates for our transmission assets and an authorized return on equity of 9.85%, and started an amortization process to return excess deferred taxes created by the TCJA. Because the approved settlement rates were lower than the proposed rates that went into effect, AES Ohio has accrued and/or paid refunds of approximately $4.5 million to users of the transmission system in the second quarter and third quarters of 2021 through credits on PJM bills.
Subsidiaries [Member]
Schedule of Regulatory Assets and Liabilities [Text Block]	Regulatory Matters Smart Grid and Comprehensive Settlement On October 23, 2020, AES Ohio entered into a Stipulation and Recommendation (settlement) with the staff of the PUCO and various customers, and organizations representing customers of AES Ohio and certain other parties with respect to, among other matters, AES Ohio's applications pending at the PUCO for (i) approval of AES Ohio's plan to modernize its distribution grid (the Smart Grid Plan), (ii) findings that AES Ohio passed the SEET for 2018 and 2019, and (iii) findings that AES Ohio's current ESP 1 satisfies the SEET and the more favorable in the aggregate (MFA) regulatory test. A hearing was held in January 2021 for consideration of this settlement and on June 16, 2021, the PUCO issued their opinion and order accepting the stipulation as filed. Applications for rehearing of the PUCO's orders relating to the comprehensive settlement were filed on July 16, 2021 and remain pending. Consistent with AES’ earlier statement of intent and based on recent discussions with AES, with the PUCO’s issuance of their opinion and order, DPL and AES Ohio expect that AES will make cash contributions of $150.0 million in 2021 to enable Smart Grid investment. Decoupling On January 23, 2020 AES Ohio filed with the PUCO requesting approval to defer its decoupling costs consistent with the methodology approved in its Distribution Rate Case. If approved, deferral would be effective December 18, 2019 and going forward would reduce impacts of weather, energy efficiency programs and economic changes in customer demand. An evidentiary hearing was held on this matter on May 4, 2021. Distribution Rate Case On November 30, 2020, AES Ohio filed a new Distribution Rate Case with the PUCO. This rate case proposes a revenue increase of $120.8 million per year and incorporates the DIR investments that were planned and approved in the last rate case but not yet included in distribution rates, other distribution investments since September 2015 and investments necessitated by the tornados that occurred on Memorial Day in 2019. The rate case also includes a proposal for increased tree-trimming expenses and certain customer demand-side management programs and recovery of prior-approved regulatory assets for tree trimming, uncollectible expenses and rate case expense. This case is pending a commission order. On July 26, 2021, the PUCO staff filed its Staff Report of Investigation in the distribution rate case. Settlement negotiations are currently ongoing, and the hearing is set to begin on December 7, 2021. FERC Proceedings On March 3, 2020, AES Ohio filed an application before the FERC to change its transmission rate from a stated rate to a formula rate, which was accepted by the FERC and made effective as of May 3, 2020, subject to further proceedings and potential refunds. An uncontested settlement was filed December 10, 2020 and approved April 15, 2021. Among other things, the settlement established new depreciation rates for our transmission assets and an authorized return on equity of 9.85%, and started an amortization process to return excess deferred taxes created by the TCJA. Because the approved settlement rates were lower than the proposed rates that went into effect, AES Ohio has accrued and/or paid refunds of approximately $4.5 million to users of the transmission system in the second quarter and third quarters of 2021 through credits on PJM bills.

Fair Value

Fair Value	9 Months Ended
	Sep. 30, 2021
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	Fair Value The fair value of current financial assets and liabilities, debt service reserves and other deposits approximate their reported carrying amounts. The estimated fair values of our assets and liabilities have been determined using available market information. By virtue of these amounts being estimates and based on hypothetical transactions to sell assets or transfer liabilities, the use of different market assumptions and/or estimation methodologies may have a material effect on the estimated fair value amounts. For further information on our valuation techniques and policies, see Note 5— Fair Value in Item 8. — Financial Statements and Supplementary Data of our Form 10-K. The following table presents the fair value, carrying value and cost of our non-derivative instruments as of September 30, 2021 and December 31, 2020. Further information about the fair value of our derivative instruments can be found in Note 4 – Derivative Instruments and Hedging Activities. September 30, 2021 December 31, 2020 $ in millions Cost Fair Value Cost Fair Value Assets Money market funds $ 0.4 $ 0.4 $ 0.3 $ 0.3 Equity securities 2.0 4.9 2.1 4.5 Debt securities 3.8 3.8 4.0 4.1 Total $ 6.2 $ 9.1 $ 6.4 $ 8.9 Carrying Value Fair Value Carrying Value Fair Value Liabilities Long-term debt $ 1,395.1 $ 1,534.0 $ 1,393.6 $ 1,571.6 These financial instruments are not subject to master netting agreements or collateral requirements and as such are presented in the Condensed Consolidated Balance Sheets at their gross fair value, except for Long-term debt, which is presented at amortized carrying value. We did not have any transfers of the fair values of our financial instruments between Level 1, Level 2 or Level 3 of the fair value hierarchy during the nine months ended September 30, 2021 or 2020. Master Trust Assets AES Ohio established a Master Trust to hold assets that could be used for the benefit of employees participating in employee benefit plans and these assets are not used for general operating purposes. These assets are primarily comprised of open-ended mutual funds, which are valued using the net asset value per unit. These investments are recorded at fair value within Other non-current assets on the Condensed Consolidated Balance Sheets and classified as equity investments. We recorded net unrealized gains / (losses) of $(0.1) million and $0.3 million during the during the three months ended September 30, 2021 and 2020, respectively, and $0.4 million and $0.0 million during the nine months ended September 30, 2021 and 2020, respectively. These amounts are included in "Other income / (expense)" in our Condensed Consolidated Statements of Operations. Long-term debt The fair value of debt is based on current public market prices for disclosure purposes only. Unrealized gains or losses are not recognized in the financial statements as long-term debt is presented at carrying value, net of unamortized premium or discount and unamortized deferred financing costs in the financial statements. The long-term debt amounts include the current portion payable in the next twelve months and have maturities that range from 2025 to 2061. The fair value of assets and liabilities as of September 30, 2021 and December 31, 2020 and the respective category within the fair value hierarchy for DPL is as follows: $ in millions Fair value as of September 30, 2021 (a) Fair value as of December 31, 2020 (a) Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Assets Master Trust assets Money market funds $ 0.4 $ — $ — $ 0.4 $ 0.3 $ — $ — $ 0.3 Equity securities — 4.9 — 4.9 — 4.5 — 4.5 Debt securities — 3.8 — 3.8 — 4.1 — 4.1 Total Master Trust assets 0.4 8.7 — 9.1 0.3 8.6 — 8.9 Total $ 0.4 $ 8.7 $ — $ 9.1 $ 0.3 $ 8.6 $ — $ 8.9 Liabilities Long-term debt $ — $ 1,516.8 $ 17.2 $ 1,534.0 $ — $ 1,554.2 $ 17.4 $ 1,571.6 Total Liabilities $ — $ 1,516.8 $ 17.2 $ 1,534.0 $ — $ 1,554.2 $ 17.4 $ 1,571.6 (a) Includes credit valuation adjustment
Subsidiaries [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	Fair Value The fair value of current financial assets and liabilities, debt service reserves and other deposits approximate their reported carrying amounts. The estimated fair values of our assets and liabilities have been determined using available market information. By virtue of these amounts being estimates and based on hypothetical transactions to sell assets or transfer liabilities, the use of different market assumptions and/or estimation methodologies may have a material effect on the estimated fair value amounts. For further information on our valuation techniques and policies, see Note 5— Fair Value in Item 8. — Financial Statements and Supplementary Data of our Form 10-K. The following table presents the fair value, carrying value and cost of our non-derivative instruments as of September 30, 2021 and December 31, 2020. Further information about the fair value of our derivative instruments can be found in Note 4 – Derivative Instruments and Hedging Activities. September 30, 2021 December 31, 2020 $ in millions Cost Fair Value Cost Fair Value Assets Money market funds $ 0.4 $ 0.4 $ 0.3 $ 0.3 Equity securities 2.0 4.9 2.1 4.5 Debt securities 3.8 3.8 4.0 4.1 Total $ 6.2 $ 9.1 $ 6.4 $ 8.9 Carrying Value Fair Value Carrying Value Fair Value Liabilities Long-term debt $ 574.2 $ 635.5 $ 574.1 $ 656.0 These financial instruments are not subject to master netting agreements or collateral requirements and as such are presented in the Condensed Balance Sheets at their gross fair value, except for Long-term debt, which is presented at amortized carrying value. We did not have any transfers of the fair values of our financial instruments between Level 1, Level 2 or Level 3 of the fair value hierarchy during the nine months ended September 30, 2021 or 2020. Master Trust Assets AES Ohio established a Master Trust to hold assets that could be used for the benefit of employees participating in employee benefit plans and these assets are not used for general operating purposes. These assets are primarily comprised of open-ended mutual funds, which are valued using the net asset value per unit. These investments are recorded at fair value within Other non-current assets on the Condensed Balance Sheets and classified as equity investments. We recorded net unrealized gains / (losses) of $(0.1) million and $0.3 million during the during the three months ended September 30, 2021 and 2020, respectively, and $0.4 million and $0.0 million during the nine months ended September 30, 2021 and 2020, respectively. These amounts are included in "Other income / (expense)" in our Condensed Statements of Operations. Long-term debt The fair value of debt is based on current public market prices for disclosure purposes only. Unrealized gains or losses are not recognized in the financial statements as long-term debt is presented at carrying value, net of unamortized premium or discount and unamortized deferred financing costs in the financial statements. The long-term debt amounts include the current portion payable in the next twelve months and have maturities that range from 2040 to 2061. The fair value of assets and liabilities as of September 30, 2021 and December 31, 2020 and the respective category within the fair value hierarchy for AES Ohio is as follows: $ in millions Fair value as of September 30, 2021 (a) Fair value as of December 31, 2020 (a) Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Assets Master Trust assets Money market funds $ 0.4 $ — $ — $ 0.4 $ 0.3 $ — $ — $ 0.3 Equity securities — 4.9 — 4.9 — 4.5 — 4.5 Debt securities — 3.8 — 3.8 — 4.1 — 4.1 Total $ 0.4 $ 8.7 $ — $ 9.1 $ 0.3 $ 8.6 $ — $ 8.9 Liabilities Long-term debt $ — $ 618.3 $ 17.2 $ 635.5 $ — $ 638.6 $ 17.4 $ 656.0 Total Liabilities $ — $ 618.3 $ 17.2 $ 635.5 $ — $ 638.6 $ 17.4 $ 656.0 (a) Includes credit valuation adjustment Our long-term debt is fair valued for disclosure purposes only and most of the fair values are determined using quoted market prices in inactive markets. These fair value inputs are considered Level 2 in the fair value hierarchy. As the Wright-Patterson Air Force Base note is not publicly traded, the fair value inputs are considered Level 3 in the fair value hierarchy as there are no observable inputs.

Derivative Instruments and Hedg

Derivative Instruments and Hedging Activities	9 Months Ended
	Sep. 30, 2021
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative Instruments and Hedging Activities	Derivative Instruments and Hedging Activities For further information on our derivative and hedge accounting policies, See Note 1 – Overview and Summary of Significant Accounting Policies – Financial Derivatives and Note 6 - Derivative Instruments and Hedging Activities of Item 8 – Financial Statements and Supplementary Data in our Form 10-K. Cash Flow Hedges In August 2020, the two interest rate swaps to hedge the variable interest on the $140.0 million variable interest rate tax-exempt First Mortgage Bonds expired, as the associated debt reached maturity. The interest rate swaps had a combined notional amount of $140.0 million and settled monthly based on a one-month LIBOR. The AOCL associated with the swaps was amortized out of AOCL into interest expense over the life of the underlying debt. We also had previously entered into interest rate derivative contracts to manage interest rate exposure related to anticipated borrowings of fixed-rate debt. These interest rate derivative contracts were settled in 2013 and we continue to amortize amounts out of AOCL into interest expense. The following tables provide information concerning gains or losses recognized in AOCL for the cash flow hedges for the three and nine months ended September 30, 2021 and 2020: Three months ended Nine months ended September 30, 2021 September 30, 2020 September 30, 2021 September 30, 2020 Interest Interest Interest Interest $ in millions (net of tax) Rate Hedge Rate Hedge Rate Hedge Rate Hedge Beginning accumulated derivative gains in AOCL $ 13.2 $ 13.9 $ 13.6 $ 14.5 Net gains associated with current period hedging transactions — 0.1 — — Net gains reclassified to earnings Interest expense (0.2) (0.3) (0.6) (0.8) Ending accumulated derivative gains in AOCL $ 13.0 $ 13.7 $ 13.0 $ 13.7 Portion expected to be reclassified to earnings in the next twelve months $ (0.8)
Subsidiaries [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative Instruments and Hedging Activities	Derivative Instruments and Hedging Activities For further information on our derivative and hedge accounting policies, See Note 1 – Overview and Summary of Significant Accounting Policies – Financial Derivatives and Note 6 - Derivative Instruments and Hedging Activities of Item 8 – Financial Statements and Supplementary Data in our Form 10-K. Cash Flow Hedges In August 2020, the two interest rate swaps to hedge the variable interest on the $140.0 million variable interest rate tax-exempt First Mortgage Bonds expired, as the associated debt reached maturity. The interest rate swaps had a combined notional amount of $140.0 million and settled monthly based on a one-month LIBOR. The AOCL associated with the swaps was amortized out of AOCL into interest expense over the life of the underlying debt. The following tables provide information concerning gains or losses recognized in AOCL for the cash flow hedges for the three and nine months ended September 30, 2020: Three months ended Nine months ended September 30, 2020 September 30, 2020 Interest Interest $ in millions (net of tax) Rate Hedge Rate Hedge Beginning accumulated derivative losses in AOCL $ (0.7) $ (0.4) Net gains associated with current period hedging transactions 0.2 0.1 Net gains reclassified to earnings Interest expense (0.1) (0.3) Ending accumulated derivative losses in AOCL $ (0.6) $ (0.6)

Debt Obligations

Debt Obligations	9 Months Ended
	Sep. 30, 2021
Debt Instrument [Line Items]
Long-term Debt	Long-term Debt Long-term debt is as follows: Interest September 30, December 31, $ in millions Rate Maturity 2021 2020 First Mortgage Bonds 3.95% 2049 $ 425.0 $ 425.0 First Mortgage Bonds 3.20% 2040 140.0 140.0 U.S. Government note 4.20% 2061 17.2 17.4 Unamortized deferred financing costs (5.5) (5.7) Unamortized debt discounts, net (2.5) (2.6) Total long-term debt at AES Ohio 574.2 574.1 Senior unsecured bonds 4.125% 2025 415.0 415.0 Senior unsecured bonds 4.35% 2029 400.0 400.0 Note to DPL Capital Trust II (a) 8.125% 2031 15.6 15.6 Unamortized deferred financing costs (8.8) (10.2) Unamortized debt discounts, net (0.9) (0.9) Total long-term debt 1,395.1 1,393.6 Less: current portion (0.2) (0.2) Long-term debt, net of current portion $ 1,394.9 $ 1,393.4 (a) Note payable to related party. Lines of credit As of September 30, 2021 and December 31, 2020, the DPL Credit Agreement had outstanding borrowings of $80.0 million and $80.0 million, respectively. As of September 30, 2021 and December 31, 2020, the AES Ohio Credit Agreement had outstanding borrowings of $140.0 million and $20.0 million, respectively. Significant transactions On July 31, 2020, AES Ohio issued $140.0 million of taxable First Mortgage Bonds and on August 3, 2020 used the proceeds to purchase at par value the $140.0 million of outstanding tax-exempt Ohio Air Quality Development Authority (OAQDA) Collateralized Pollution Control Revenue Refunding Bonds that had been issued in 2015. The new taxable First Mortgage Bonds carry an interest rate of 3.20% and mature on July 31, 2040. The OAQDA Revenue bonds have not been legally cancelled and can be re-issued at the discretion of AES Ohio at any time. These bonds will be held in trust while we continue to evaluate market conditions and explore suitable long-term financing alternatives. Accordingly, as of September 30, 2021 and December 31, 2020, the $140.0 million variable rate OAQDA Revenue bonds are not treated as being outstanding in the Condensed Consolidated Balance Sheet. On June 19, 2020, DPL closed a $415.0 million issuance of senior unsecured notes. These notes carry an interest rate of 4.125% and mature on July 1, 2025. Proceeds from the issuance and cash on hand were used to redeem in-full the remaining balance of $380.0 million of DPL's 7.25% senior unsecured notes. These bonds were redeemed at par plus accrued interest and a make-whole premium of $30.8 million on July 20, 2020. DPL agreed to register the 2025 DPL Senior Unsecured Bonds under the Securities Act by filing an exchange offer registration statement or, under specified circumstances, a shelf registration statement with the SEC pursuant to a Registration Rights Agreement dated June 19, 2020. DPL filed a registration statement on Form S-4 with respect to the 2025 DPL Senior Unsecured Bonds with the SEC on March 15, 2021, and this registration statement was declared effective on March 31, 2021. The exchange offer closed on May 5, 2021. On June 1, 2020, the DPL Credit Agreement was amended. As a result of the amendment, the borrowing limit was reduced from $125.0 million to $110.0 million, the Total Debt to EBITDA covenant was eliminated, the EBITDA to Interest Expense covenant was reduced from 2.25 to 1.00 to 1.70 to 1.00, increasing to 1.75 to 1.00 as of September 30, 2022 and 2.00 to 1.00 as of December 31, 2022, and a trailing-twelve months minimum EBITDA covenant of $125.0 million was added, increasing to $130.0 million as of September 30, 2022 and $150.0 million as of December 31, 2022. Starting with the quarter ended September 30, 2021, the borrowing limit will be reduced by $5.0 million per quarter should DPL’s Total Debt to EBITDA ratio calculated for the period of four consecutive quarters exceed 7.00 to 1.00. Long-term debt covenants and restrictions The DPL Credit Agreement has two financial covenants. The first financial covenant, a minimum EBITDA, calculated at the end of each fiscal quarter for the four prior fiscal quarters, of $125.0 million is required, stepping up to $130.0 million on September 30, 2022 and $150.0 million on December 31, 2022. As of September 30, 2021, DPL was in compliance with this financial covenant. The second financial covenant is an EBITDA to Interest Expense ratio that is calculated, at the end of each fiscal quarter, by dividing EBITDA for the four prior fiscal quarters by the consolidated interest charges for the same period. The ratio, per the agreement, is to be not less than 1.70 to 1.00, and steps up to 1.75 to 1.00 on September 30, 2022 and 2.00 to 1.00 as of December 31, 2022. As of September 30, 2021, DPL was in compliance with this financial covenant. The DPL Credit Agreement also restricts dividend payments from DPL to AES, such that DPL cannot make dividend payments unless at the time of, and/or as a result of the distribution, (i) DPL’s leverage ratio does not exceed 0.67 to 1.00 and DPL’s interest coverage ratio is not less than 2.50 to 1.00 or, if such ratios are not within the parameters, (ii) DPL’s senior long-term debt rating from two of the three major credit rating agencies is at least investment grade. As a result, as of September 30, 2021, DPL was prohibited from making a distribution to its shareholder or making a loan to any of its affiliates (other than its subsidiaries). Starting with the quarter ended September 30, 2021, the borrowing limit on the DPL Credit Agreement will be reduced by $5.0 million per quarter should the Total Debt to EBITDA ratio for the period of four consecutive quarters exceed 7.00 to 1.00. As of September 30, 2021, DPL exceeded this ratio and the borrowing limit was reduced from $110.0 million to $105.0 million. The AES Ohio Credit Agreement and Bond Purchase Agreement (financing document entered into in connection with the issuance of AES Ohio's First Mortgage Bonds, on July 31, 2020) has one financial covenant. The covenant measures Total Debt to Total Capitalization and is calculated, at the end of each fiscal quarter, by dividing total debt at the end of the quarter by total capitalization at the end of the quarter. AES Ohio’s Total Debt to Total Capitalization ratio shall not be greater than 0.67 to 1.00. As of September 30, 2021, AES Ohio was in compliance with this financial covenant. As of September 30, 2021, DPL and AES Ohio were in compliance with all debt covenants, including the financial covenants described above. AES Ohio does not have any meaningful restrictions in its debt financing documents prohibiting dividends and return of capital payments to its parent, DPL. Substantially all property, plant & equipment of AES Ohio is subject to the lien of the mortgage securing AES Ohio’s First and Refunding Mortgage.
Subsidiaries [Member]
Debt Instrument [Line Items]
Long-term Debt	Long-term Debt Long-term debt is as follows: Interest September 30, December 31, $ in millions Rate Maturity 2021 2020 First Mortgage Bonds 3.95 % 2049 $ 425.0 $ 425.0 First Mortgage Bonds 3.20 % 2040 140.0 140.0 U.S. Government note 4.20 % 2061 17.2 17.4 Unamortized deferred financing costs (5.5) (5.7) Unamortized debt discounts, net (2.5) (2.6) Total long-term debt 574.2 574.1 Less: current portion (0.2) (0.2) Long-term debt, net of current portion $ 574.0 $ 573.9 Line of credit As of September 30, 2021 and December 31, 2020, the AES Ohio Credit Agreement had outstanding borrowings on its line of credit of $140.0 million and $20.0 million, respectively. Significant transactions On July 31, 2020, AES Ohio issued $140.0 million of taxable First Mortgage Bonds and on August 3, 2020 used the proceeds to purchase at par value the $140.0 million of outstanding tax-exempt Ohio Air Quality Development Authority (OAQDA) Collateralized Pollution Control Revenue Refunding Bonds that had been issued in 2015. The new taxable First Mortgage Bonds carry an interest rate of 3.20% and mature on July 31, 2040. The OAQDA Revenue bonds have not been legally cancelled and can be re-issued at the discretion of AES Ohio at any time. These bonds will be held in trust while we continue to evaluate market conditions and explore suitable long-term financing alternatives. Accordingly, as of September 30, 2021 and December 31, 2020, the $140.0 million variable rate OAQDA Revenue bonds are not treated as being outstanding in the Condensed Consolidated Balance Sheet. Long-term debt covenants and restrictions The AES Ohio Credit Agreement and Bond Purchase Agreement (financing document entered into in connection with the issuance of AES Ohio's First Mortgage Bonds, on July 31, 2020) has one financial covenant. The covenant measures Total Debt to Total Capitalization and is calculated, at the end of each fiscal quarter, by dividing total debt at the end of the quarter by total capitalization at the end of the quarter. AES Ohio’s Total Debt to Total Capitalization ratio shall not be greater than 0.67 to 1.00. As of September 30, 2021, AES Ohio was in compliance with this financial covenant. As of September 30, 2021, AES Ohio was in compliance with all debt covenants, including the financial covenants described above. AES Ohio does not have any meaningful restrictions in its debt financing documents prohibiting dividends and return of capital payments to its parent, DPL. Substantially all property, plant & equipment of AES Ohio is subject to the lien of the mortgage securing AES Ohio’s First and Refunding Mortgage.

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2021
Entity Information [Line Items]
Income Taxes	Income Taxes DPL's provision for income taxes is based on the estimated annual effective tax rate, plus discrete items. The effective tax rates for the three and nine months ended September 30, 2021 were (10.4)% and (1.8)%, respectively, and 55.2% and 71.1% for the three and nine months ended September 30, 2020, respectively. The year-to-date rate is different from the combined federal and state statutory rate of 22.5% primarily due to the flowthrough of the net tax benefit related to the reversal of excess deferred taxes of AES Ohio as a percentage of pre-tax book income. DPL's income tax expense for the nine months ended September 30, 2021 was calculated using the estimated annual effective income tax rates for 2021 of (1.8)%. Management estimates the annual effective tax rate based on its forecast of annual pre-tax income or loss. DPL has unrecognized tax benefits of $1.4 million as of September 30, 2021 and December 31, 2020. The total amount of unrecognized tax benefits anticipated to result in a net decrease to unrecognized tax benefits within twelve months of September 30, 2021 is estimated to be $1.4 million, primarily relating to effective settlements of tax exams. Of the $1.4 million, $0.5 million would result in a decrease in the effective tax rate in the period that the position is released. AES files federal and state income tax returns which consolidate DPL and its subsidiaries. Under a tax sharing agreement with AES, DPL is responsible for the income taxes associated with its own taxable income and records the provision for income taxes using a separate return method.
Subsidiaries [Member]
Entity Information [Line Items]
Income Taxes	Income Taxes AES Ohio's provision for income taxes is based on the estimated annual effective tax rate, plus discrete items. The effective tax rates for the three and nine months ended September 30, 2021 were 16.8% and 13.7%, respectively, and 16.4% and 4.8% for the three and nine months ended September 30, 2020, respectively. The year-to-date rate is different from the combined federal and state statutory rate of 22.5% primarily due to the flowthrough of the net tax benefit related to the reversal of excess deferred taxes of AES Ohio as a percentage of pre-tax book income. AES Ohio has unrecognized tax benefits of $1.4 million as of September 30, 2021 and December 31, 2020. The total amount of unrecognized tax benefits anticipated to result in a net decrease to unrecognized tax benefits within twelve months of September 30, 2021 is estimated to be $1.4 million, primarily relating to effective settlements of tax exams. Of the $1.4 million, $0.5 million would result in a decrease in the effective tax rate in the period that the position is released.

Benefit Plans

Benefit Plans	9 Months Ended
	Sep. 30, 2021
Pension [Member]
Entity Information [Line Items]
Pension and Postretirement Benefits	Benefit Plans AES Ohio sponsors a defined benefit pension plan for the majority of its employees. We generally fund pension plan benefits as accrued in accordance with the minimum funding requirements of ERISA and, in addition, make voluntary contributions from time to time. There were $9.8 million and $7.5 million in employer contributions during the nine months ended September 30, 2021 and 2020, respectively. The amounts presented in the following tables for pension include the collective bargaining plan formula, the traditional management plan formula, the cash balance plan formula and the SERP, in the aggregate. The pension costs below have not been adjusted for amounts billed to the Service Company for former AES Ohio employees who are now employed by the Service Company or other AES affiliates that are still participants in the AES Ohio plan. The components of net periodic benefit costs other than service costs are included in Other income / (expense) in the Condensed Consolidated Statements of Operations. The net periodic benefit cost of the pension benefit plans for the three and nine months ended September 30, 2021 and 2020 was: Three months ended Nine months ended September 30, September 30, $ in millions 2021 2020 2021 2020 Service cost $ 1.2 $ 0.9 $ 3.4 $ 2.8 Interest cost 2.1 2.9 6.1 8.8 Expected return on plan assets (3.8) (4.6) (11.2) (14.0) Amortization of unrecognized: Prior service cost 0.2 0.3 0.6 0.8 Actuarial loss 2.2 1.5 6.8 4.6 Net periodic benefit cost $ 1.9 $ 1.0 $ 5.7 $ 3.0 In addition, AES Ohio provides postretirement health care and life insurance benefits to certain retired employees, their spouses and eligible dependents. We have funded a portion of the union-eligible benefits using a Voluntary Employee Beneficiary Association Trust. These postretirement health care benefits and the related unfunded obligation of $8.3 million as of September 30, 2021 and $9.0 million as of December 31, 2020 were not material to the financial statements in the periods covered by this report.
Subsidiaries [Member]
Entity Information [Line Items]
Pension and Postretirement Benefits	Benefit Plans AES Ohio sponsors a defined benefit pension plan for the majority of its employees. We generally fund pension plan benefits as accrued in accordance with the minimum funding requirements of ERISA and, in addition, make voluntary contributions from time to time. There were $9.8 million and $7.5 million in employer contributions during the nine months ended September 30, 2021 and 2020, respectively. The amounts presented in the following tables for pension include the collective bargaining plan formula, the traditional management plan formula, the cash balance plan formula and the SERP, in the aggregate. The pension costs below have not been adjusted for amounts billed to the Service Company for former AES Ohio employees who are now employed by the Service Company or other AES affiliates or for amounts billed to AES Ohio Generation for former employees that were employed by AES Ohio Generation that are still participants in the AES Ohio plan. The components of net periodic benefit costs other than service costs are included in Other income / (expense) in the Condensed Statements of Operations. The net periodic benefit cost of the pension benefit plans for the three and nine months ended September 30, 2021 and 2020 was: Three months ended Nine months ended September 30, September 30, $ in millions 2021 2020 2021 2020 Service cost $ 1.2 $ 0.9 $ 3.4 $ 2.8 Interest cost 2.1 2.9 6.1 8.8 Expected return on plan assets (3.8) (4.6) (11.2) (14.0) Amortization of unrecognized: Prior service cost 0.2 0.3 0.8 1.0 Actuarial loss 2.9 2.2 8.5 6.5 Net periodic benefit cost $ 2.6 $ 1.7 $ 7.6 $ 5.1 In addition, AES Ohio provides postretirement health care and life insurance benefits to certain retired employees, their spouses and eligible dependents. We have funded a portion of the union-eligible benefits using a Voluntary Employee Beneficiary Association Trust. These postretirement health care benefits and the related unfunded obligation of $8.3 million as of September 30, 2021 and $9.0 million as of December 31, 2020 were not material to the financial statements in the periods covered by this report.

Statement of Shareholders' Equi

Statement of Shareholders' Equity	9 Months Ended
	Sep. 30, 2021
Statement of Stockholders' Equity [Abstract]
Stockholders' Equity Note Disclosure	Shareholder's Deficit Capital Contributions from AES There were no capital contributions during the nine months ended September 30, 2021. During the nine months ended September 30, 2020, DPL received $150.0 million in a cash contribution from AES, which DPL then used to make a $150.0 million capital contribution to AES Ohio . The contribution at DPL represented an equity capital contribution of $98.0 million and a payment of $52.0 million against its tax receivable. The proceeds from the capital contribution at AES Ohio will primarily be used for funding needs to support AES Ohio's capital expenditure program, mainly new investments in and upgrades to AES Ohio’s transmission and distribution system.

Contractual Obligations, Commer

Contractual Obligations, Commercial Commitments and Contingencies	9 Months Ended
	Sep. 30, 2021
Entity Information [Line Items]
Contractual Obligations, Commercial Commitments and Contingencies	Contractual Obligations, Commercial Commitments and Contingencies Equity Ownership Interest AES Ohio has a 4.9% equity ownership interest in OVEC, which is recorded using the cost method of accounting under GAAP. AES Ohio , along with several non-affiliated energy companies party to an OVEC arrangement, receive and pay for OVEC capacity and energy and are responsible for OVEC debt obligations and other fixed costs in proportion to their power participation ratios under the arrangement, which, for AES Ohio, is the same as its equity ownership interest. As of September 30, 2021, AES Ohio could be responsible for the repayment of 4.9%, or $55.9 million, of $1,140.5 million OVEC debt obligations if they came due, comprised of both fixed and variable rate securities with maturities from 2022 to 2040. OVEC could also seek additional contributions from AES Ohio to avoid a default in the event that other OVEC members defaulted on their respective OVEC obligations. Contingencies In the normal course of business, we are subject to various lawsuits, actions, proceedings, claims and other matters asserted under various laws and regulations. We believe the amounts provided in our Condensed Consolidated Financial Statements, as prescribed by GAAP, are adequate considering the probable and estimable contingencies. However, there can be no assurances that the actual amounts required to satisfy alleged liabilities from various legal proceedings, claims, tax examinations and other matters discussed below, and to comply with applicable laws and regulations, will not exceed the amounts reflected in our Condensed Consolidated Financial Statements. As such, costs, if any, that may be incurred in excess of those amounts provided as of September 30, 2021, cannot be reasonably determined. Environmental Matters DPL’s and AES Ohio’s current and previously-owned facilities and operations are subject to a wide range of federal, state and local environmental regulations and laws. The environmental issues that may affect us include: • The federal CAA and state laws and regulations (including State Implementation Plans) which require compliance, obtaining permits and reporting as to air emissions; • Litigation with federal and certain state governments and certain special interest groups regarding whether modifications to or maintenance of certain coal-fired generating stations require additional permitting or pollution control technology, or whether emissions from coal-fired generating stations cause or contribute to global climate changes; • Rules and future rules issued by the USEPA, the Ohio EPA or other authorities that require or will require substantial reductions in SO2, particulates, mercury, acid gases, NOx and other air emissions; • Rules and future rules issued by the USEPA, the Ohio EPA or other authorities that require or will require reporting and reductions of GHGs; • Rules and future rules issued by the USEPA, the Ohio EPA or other authorities associated with the federal Clean Water Act, which prohibits the discharge of pollutants into waters of the United States except pursuant to appropriate permits; and • Solid and hazardous waste laws and regulations, which govern the management and disposal of certain waste. The majority of solid waste created from the combustion of coal and fossil fuels consists of fly ash and other coal combustion by-products. In addition to imposing continuing compliance obligations, federal, state and local environmental laws and regulations authorize the imposition of substantial penalties for noncompliance, including fines, injunctive relief and other sanctions. In the normal course of business, we have investigatory and remedial activities underway at our facilities to comply, or to determine compliance, with such regulations. We record liabilities for loss contingencies related to environmental matters when a loss is probable of occurring and can be reasonably estimated in accordance with the provisions of GAAP. Accordingly, we have immaterial accruals for loss contingencies for environmental matters. We also have several environmental matters for which we have not accrued loss contingencies because the risk of loss is not probable, or a loss cannot be reasonably estimated. We evaluate the potential liability related to environmental matters quarterly and may revise our estimates. Such revisions in the estimates of the potential liabilities could have a material adverse effect on our results of operations, financial condition and cash flows. We have several pending environmental matters associated with our previously-owned and operated coal-fired generation units. Some of these matters could have a material adverse effect on our results of operations, financial condition and cash flows.
Subsidiaries [Member]
Entity Information [Line Items]
Contractual Obligations, Commercial Commitments and Contingencies	Contractual Obligations, Commercial Commitments and Contingencies Equity Ownership Interest AES Ohio has a 4.9% equity ownership interest in OVEC, which is recorded using the cost method of accounting under GAAP. AES Ohio , along with several non-affiliated energy companies party to an OVEC arrangement, receive and pay for OVEC capacity and energy and are responsible for OVEC debt obligations and other fixed costs in proportion to their power participation ratios under the arrangement, which, for AES Ohio, is the same as its equity ownership interest. As of September 30, 2021, AES Ohio could be responsible for the repayment of 4.9%, or $55.9 million, of $1,140.5 million OVEC debt obligations if they came due, comprised of both fixed and variable rate securities with maturities from 2022 to 2040. OVEC could also seek additional contributions from AES Ohio to avoid a default in the event that other OVEC members defaulted on their respective OVEC obligations. Contingencies In the normal course of business, we are subject to various lawsuits, actions, proceedings, claims and other matters asserted under various laws and regulations. We believe the amounts provided in our Condensed Financial Statements, as prescribed by GAAP, are adequate considering the probable and estimable contingencies. However, there can be no assurances that the actual amounts required to satisfy alleged liabilities from various legal proceedings, claims, tax examinations and other matters discussed below, and to comply with applicable laws and regulations, will not exceed the amounts reflected in our Condensed Financial Statements. As such, costs, if any, that may be incurred in excess of those amounts provided as of September 30, 2021, cannot be reasonably determined. Environmental Matters AES Ohio’s current and previously-owned facilities and operations are subject to a wide range of federal, state and local environmental regulations and laws. The environmental issues that may affect us include: • The federal CAA and state laws and regulations (including State Implementation Plans) which require compliance, obtaining permits and reporting as to air emissions; • Litigation with federal and certain state governments and certain special interest groups regarding whether modifications to or maintenance of certain coal-fired generating stations require additional permitting or pollution control technology, or whether emissions from coal-fired generating stations cause or contribute to global climate changes; • Rules and future rules issued by the USEPA, the Ohio EPA or other authorities that require or will require substantial reductions in SO2, particulates, mercury, acid gases, NOx and other air emissions; • Rules and future rules issued by the USEPA, the Ohio EPA or other authorities that require or will require reporting and reductions of GHGs; • Rules and future rules issued by the USEPA, the Ohio EPA or other authorities associated with the federal Clean Water Act, which prohibits the discharge of pollutants into waters of the United States except pursuant to appropriate permits; and • Solid and hazardous waste laws and regulations, which govern the management and disposal of certain waste. In addition to imposing continuing compliance obligations, federal, state and local environmental laws and regulations authorize the imposition of substantial penalties for noncompliance, including fines, injunctive relief and other sanctions. In the normal course of business, we have investigatory and remedial activities underway at our facilities to comply, or to determine compliance, with such regulations. We record liabilities for loss contingencies related to environmental matters when a loss is probable of occurring and can be reasonably estimated in accordance with the provisions of GAAP. Accordingly, we have immaterial accruals for loss contingencies for environmental matters. We also have several environmental matters for which we have not accrued loss contingencies because the risk of loss is not probable, or a loss cannot be reasonably estimated. We evaluate the potential liability related to environmental matters quarterly and may revise our estimates. Such revisions in the estimates of the potential liabilities could have a material adverse effect on our results of operations, financial condition and cash flows.

Business Segments

Business Segments	9 Months Ended
	Sep. 30, 2021
Segment Reporting Information [Line Items]
Business Segments	Business Segments DPL manages its business through one reportable operating segment, the Utility segment. The primary segment performance measure is income / (loss) from continuing operations before income tax as management has concluded that this measure best reflects the underlying business performance of DPL and is the most relevant measure considered in DPL’s internal evaluation of the financial performance of its segment. The Utility segment is discussed further below. Utility Segment The Utility segment is comprised of AES Ohio’s electric transmission and distribution businesses, which distribute electricity to residential, commercial, industrial and governmental customers. AES Ohio distributes electricity to approximately 533,000 retail customers located in a 6,000-square mile area of West Central Ohio. AES Ohio’s electric transmission and distribution businesses are subject to rate regulation by federal and state regulators. Accordingly, AES Ohio applies the accounting standards for regulated operations to its electric transmission and distribution businesses recording regulatory assets when incurred costs are expected to be recovered in future customer rates and regulatory liabilities when current cost recoveries in customer rates relate to expected future costs. The Utility segment includes revenues and costs associated with our investment in OVEC and the historical results of AES Ohio’s Hutchings Coal Station, which was closed in 2013 and transferred to a third party in the fourth quarter of 2020. Included within the “Other” column are other businesses that do not meet the GAAP requirements for disclosure as reportable segments as well as certain corporate costs, which include interest expense on DPL's long-term debt as well as adjustments related to purchase accounting from the Merger. The accounting policies of the reportable segment are the same as those described in Note 1 – Overview and Summary of Significant Accounting Policies of our 10-K. Intersegment sales, costs of sales and expenses are eliminated in consolidation. Certain shared and corporate costs are allocated between "Other" and the Utility reporting segment. The following tables present financial information for DPL’s Utility reportable business segment: $ in millions Utility Other Adjustments and Eliminations DPL Consolidated Three months ended September 30, 2021 Revenues from external customers $ 185.9 $ 2.3 $ — $ 188.2 Intersegment revenues 0.2 0.8 (1.0) — Total revenues $ 186.1 $ 3.1 $ (1.0) $ 188.2 Depreciation and amortization $ 18.6 $ 0.3 $ — $ 18.9 Interest expense $ 6.1 $ 9.7 $ — $ 15.8 Income / (loss) from continuing operations before income tax $ 16.1 $ (8.4) $ — $ 7.7 $ in millions Utility Other Adjustments and Eliminations DPL Consolidated Three Months Ended September 30, 2020 Revenues from external customers $ 176.8 $ 2.0 $ — $ 178.8 Intersegment revenues 0.2 1.0 (1.2) — Total revenues $ 177.0 $ 3.0 $ (1.2) $ 178.8 Depreciation and amortization $ 18.2 $ 0.4 $ — $ 18.6 Interest expense $ 5.9 $ 11.2 $ — $ 17.1 Loss on early extinguishment of debt $ — $ 31.7 $ — $ 31.7 Income / (loss) from continuing operations before income tax $ 21.3 $ (41.0) $ — $ (19.7) $ in millions Utility Other Adjustments and Eliminations DPL Consolidated Nine months ended September 30, 2021 Revenues from external customers $ 504.2 $ 7.3 $ 511.5 Intersegment revenues 0.6 2.6 (3.2) — Total revenues $ 504.8 $ 9.9 $ (3.2) $ 511.5 Depreciation and amortization $ 55.8 $ 1.1 $ — $ 56.9 Interest expense $ 18.1 $ 28.9 $ — $ 47.0 Income / (loss) from continuing operations before income tax $ 46.7 $ (23.6) $ — $ 23.1 $ in millions Utility Other Adjustments and Eliminations DPL Consolidated Nine months ended September 30, 2020 Revenues from external customers $ 498.4 $ 6.7 $ — $ 505.1 Intersegment revenues 0.7 2.7 (3.4) — Total revenues $ 499.1 $ 9.4 $ (3.4) $ 505.1 Depreciation and amortization $ 53.7 $ 1.1 $ — $ 54.8 Interest expense $ 18.5 $ 36.9 $ — $ 55.4 Loss on early extinguishment of debt $ — $ 31.7 $ — $ 31.7 Income / (loss) from continuing operations before income tax $ 49.7 $ (63.3) $ — $ (13.6) Total Assets September 30, 2021 December 31, 2020 Utility $ 2,067.6 $ 2,014.7 All Other (a) 21.1 21.3 DPL Consolidated $ 2,088.7 $ 2,036.0

Revenue (Notes)

Revenue (Notes)	9 Months Ended
	Sep. 30, 2021
Revenue from Contract with Customer [Text Block]	Revenue Revenue is primarily earned from retail and wholesale electricity sales and electricity transmission and distribution delivery services. Revenue is recognized upon transfer of control to customers in an amount that reflects the consideration to which we expect to be entitled in exchange for those goods or services. Revenue is recorded net of any taxes assessed on and collected from customers, which are remitted to the governmental authorities. For further discussion of our Retail, Wholesale, RTO ancillary, and Capacity revenues, see Note 14 — Revenue in Item 8.— Financial Statements and Supplementary Data of our Form 10-K. DPL's revenue from contracts with customers was $187.5 million and $177.0 million for the three months ended September 30, 2021 and 2020, respectively; and $507.0 million and $492.3 million for the nine months ended September 30, 2021 and 2020, respectively. The following table presents our revenue from contracts with customers and other revenue by segment for the three and nine months ended September 30, 2021 and 2020: $ in millions Utility Other Adjustments and Eliminations Total Three Months Ended September 30, 2021 Retail revenue Retail revenue from contracts with customers Residential revenue $ 103.3 $ — $ — $ 103.3 Commercial revenue 35.0 — — 35.0 Industrial revenue 16.0 — — 16.0 Governmental revenue 7.0 — — 7.0 Other (a) 2.9 — — 2.9 Total retail revenue from contracts with customers 164.2 — — 164.2 Wholesale revenue Wholesale revenue from contracts with customers 6.8 — (0.2) 6.6 RTO ancillary revenue 12.5 — — 12.5 Capacity revenue 1.8 — — 1.8 Miscellaneous revenue Miscellaneous revenue from contracts with customers (c) — 2.4 — 2.4 Other miscellaneous revenue 0.8 0.7 (0.8) 0.7 Total revenues $ 186.1 $ 3.1 $ (1.0) $ 188.2 $ in millions Utility Other Adjustments and Eliminations Total Three Months Ended September 30, 2020 Retail revenue Retail revenue from contracts with customers Residential revenue $ 99.3 $ — $ — $ 99.3 Commercial revenue 32.2 — — 32.2 Industrial revenue 14.5 — — 14.5 Governmental revenue 9.9 — — 9.9 Other (a) 3.7 — — 3.7 Total retail revenue from contracts with customers 159.6 — — 159.6 Other retail revenue (b) 0.1 — — 0.1 Wholesale revenue Wholesale revenue from contracts with customers 3.2 — (0.2) 3.0 RTO ancillary revenue 11.5 (0.1) — 11.4 Capacity revenue 0.9 — — 0.9 Miscellaneous revenue Miscellaneous revenue from contracts with customers (c) — 2.1 — 2.1 Other miscellaneous revenue 1.7 1.0 (1.0) 1.7 Total revenues $ 177.0 $ 3.0 $ (1.2) $ 178.8 Nine months ended September 30, 2021 Retail revenue Retail revenue from contracts with customers Residential revenue $ 279.3 $ — $ — $ 279.3 Commercial revenue 90.5 — — 90.5 Industrial revenue 42.4 — — 42.4 Governmental revenue 19.9 — — 19.9 Other (a) 9.4 — — 9.4 Total retail revenue from contracts with customers 441.5 — — 441.5 Wholesale revenue Wholesale revenue from contracts with customers 15.4 — (0.6) 14.8 RTO ancillary revenue 39.4 0.1 — 39.5 Capacity revenue 4.0 — — 4.0 Miscellaneous revenue Miscellaneous revenue from contracts with customers (c) — 7.2 — 7.2 Other miscellaneous revenue 4.5 2.6 (2.6) 4.5 Total revenues $ 504.8 $ 9.9 $ (3.2) $ 511.5 Nine months ended September 30, 2020 Retail revenue Retail revenue from contracts with customers Residential revenue $ 279.9 $ — $ — $ 279.9 Commercial revenue 87.6 — — 87.6 Industrial revenue 38.2 — — 38.2 Governmental revenue 27.7 — — 27.7 Other (a) 9.7 — — 9.7 Total retail revenue from contracts with customers 443.1 — — 443.1 Other retail revenue (b) 8.8 — — 8.8 Wholesale revenue Wholesale revenue from contracts with customers 7.7 — (0.7) 7.0 RTO ancillary revenue 32.3 — — 32.3 Capacity revenue 3.2 — — 3.2 Miscellaneous revenue Miscellaneous revenue from contracts with customers (c) — 6.7 — 6.7 Other miscellaneous revenue 4.0 2.7 (2.7) 4.0 Total revenues $ 499.1 $ 9.4 $ (3.4) $ 505.1 (a) "Other" primarily includes Wright-Patterson Air Force Base revenues, billing service fees from CRES providers and other miscellaneous retail revenues from contracts with customers. (b) Other retail revenue includes alternative revenue programs not accounted for under FASC 606. (c) Miscellaneous revenue from contracts with customers primarily includes revenues for various services provided by Miami Valley Lighting. The balances of receivables from contracts with customers were $62.9 million and $70.1 million as of September 30, 2021 and December 31, 2020, respectively. Payment terms for all receivables from contracts with customers are typically within 30 days.
Subsidiaries [Member]
Revenue from Contract with Customer [Text Block]	Revenue Revenue is primarily earned from retail and wholesale electricity sales and electricity transmission and distribution delivery services. Revenue is recognized upon transfer of control to customers in an amount that reflects the consideration to which we expect to be entitled in exchange for those goods or services. Revenue is recorded net of any taxes assessed on and collected from customers, which are remitted to the governmental authorities. For further discussion of our Retail, Wholesale, RTO ancillary, and Capacity revenues, see Note 13 — Revenue in Item 8.— Financial Statements and Supplementary Data of our Form 10-K. AES Ohio's revenue from contracts with customers was $185.3 million and $175.2 million for the three months ended September 30, 2021 and 2020, respectively; and $500.3 million and $486.3 million for the nine months ended September 30, 2021 and 2020, respectively. The following table presents our revenue from contracts with customers and other revenue for the three and nine months ended September 30, 2021 and 2020: Three months ended Nine months ended September 30, September 30, $ in millions 2021 2020 2021 2020 Retail revenue Retail revenue from contracts with customers Residential revenue $ 103.3 $ 99.3 $ 279.3 $ 279.9 Commercial revenue 35.0 32.2 90.5 87.6 Industrial revenue 16.0 14.5 42.4 38.2 Governmental revenue 7.0 9.9 19.9 27.7 Other (a) 2.9 3.7 9.4 9.7 Total retail revenue from contracts with customers 164.2 159.6 441.5 443.1 Other retail revenue (b) — 0.1 — 8.8 Wholesale revenue Wholesale revenue from contracts with customers 6.8 3.2 15.4 7.7 RTO ancillary revenue 12.5 11.5 39.4 32.3 Capacity revenue 1.8 0.9 4.0 3.2 Miscellaneous revenue 0.8 1.7 4.5 4.0 Total revenues $ 186.1 $ 177.0 $ 504.8 $ 499.1 (a) "Other" primarily includes Wright-Patterson Air Force Base revenues, billing service fees from CRES providers and other miscellaneous retail revenues from contracts with customers. (b) Other retail revenue includes alternative revenue programs not accounted for under FASC 606. The balances of receivables from contracts with customers were $62.2 million and $69.2 million as of September 30, 2021 and December 31, 2020, respectively. Payment terms for all receivables from contracts with customers are typically within 30 days.

Discontinued Operations

Discontinued Operations	9 Months Ended
	Sep. 30, 2021
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Discontinued Operations	Discontinued Operations Conesville - In May 2020, AEP, the operator of the formerly co-owned Conesville EGU, retired Conesville Unit 4 as planned. On June 5, 2020, DPL and AES Ohio Generation, together with AEP, completed the transfer of their interests in the retired Unit 4, including the associated environmental liabilities, to an unaffiliated third-party purchaser. For the transaction, DPL will make quarterly cash expenditures, totaling $4.0 million, through July 2022, of which $3.0 million has been paid through September 30, 2021. The transfer of Conesville Unit 4 was the last step in DPL's plan to exit its AES Ohio Generation business operations. DPL determined that the transfer of Conesville and the previous transfers and sales of other AES Ohio Generation assets constitute the disposal of a group of components, which, as a whole, represent a strategic shift to exit its AES Ohio Generation business. As such, the disposal of this group of components qualifies to be presented as discontinued operations. Therefore, the results of operations of this group of components have been reported as such in the Condensed Consolidated Statements of Operations for all periods presented. The following table summarizes the revenues, operating costs, other expenses and income tax of discontinued operations for the periods indicated: Three months ended Nine months ended September 30, September 30, $ in millions 2021 2020 2021 2020 Revenues $ — $ 0.9 $ 1.4 $ 23.3 Operating costs and other expenses — 0.5 (2.4) (23.9) Loss from discontinued operations before income tax — 1.4 (1.0) (0.6) Gain from disposal of discontinued operations — — — 4.5 Income tax expense / (benefit) from discontinued operations — 0.3 (0.2) 0.8 Net income / (loss) from discontinued operations $ — $ 1.1 $ (0.8) $ 3.1 Cash flows related to discontinued operations are included in our Condensed Consolidated Statements of Cash Flows. Cash flows from operating activities for discontinued operations were $0.4 million and $1.5 million for the three months ended September 30, 2021 and 2020, respectively, and $0.4 million and $5.1 million for the nine months ended September 30, 2021 and 2020, respectively. Cash flows from investing activities for discontinued operations were $(0.4) million and $(0.4) million for the three months ended September 30, 2021 and 2020, respectively, and $(1.2) million and $4.0 million for the nine months ended September 30, 2021 and 2020, respectively.

Risk & Uncertainties (Notes)

Risk & Uncertainties (Notes)	9 Months Ended
	Sep. 30, 2021
Unusual Risk or Uncertainty [Line Items]
Risks and Uncertainties [Text Block]	Risks and Uncertainties COVID-19 Pandemic The COVID-19 pandemic has impacted global economic activity, including electricity and energy consumption, and caused significant volatility in financial markets. Many countries, including the U.S., reacted to the pandemic by instituting quarantines and mandating business and school closures or limitations and other social distancing measures. Responses to the COVID-19 pandemic by the State of Ohio and its residents and businesses continue to evolve as vaccine availability and usage continues and the State and businesses review and adjust the scope and requirements of social distancing measures. Social distancing measures designed to slow the spread of the virus, such as business closures and operations limitations, impact energy demand within our service territory. We continue to take a variety of measures in response to the spread of COVID-19 to ensure our ability to transmit, distribute and sell electric energy, ensure the health and safety of our employees, contractors, customers and
Subsidiaries [Member]
Unusual Risk or Uncertainty [Line Items]
Risks and Uncertainties [Text Block]	Risks and Uncertainties COVID-19 Pandemic The COVID-19 pandemic has impacted global economic activity, including electricity and energy consumption, and caused significant volatility in financial markets. Many countries, including the U.S., reacted to the pandemic by instituting quarantines and mandating business and school closures or limitations and other social distancing measures. Responses to the COVID-19 pandemic by the State of Ohio and its residents and businesses continue to evolve as vaccine availability and usage continues and the State and businesses review and adjust the scope and requirements of social distancing measures. Social distancing measures designed to slow the spread of the virus, such as business closures and operations limitations, impact energy demand within our service territory. We continue to take a variety of measures in response to the spread of COVID-19 to ensure our ability to transmit, distribute and sell electric energy, ensure the health and safety of our employees, contractors, customers and communities and provide essential services to the communities in which we operate. In addition to the impacts to demand within our service territory, we also have incurred and expect to continue to incur expenses relating to COVID-19, including those that relate to events outside of our control. The magnitude and duration of the COVID-19

Summary of Significant Accounti

Summary of Significant Accounting Policies (Policy)	9 Months Ended
	Sep. 30, 2021
Significant Accounting Policies [Line Items]
Description of Business	Description of Business DPL is a regional energy company organized in 1985 under the laws of Ohio. DPL has one reportable segment, the Utility segment. See Note 10 – Business Segments for more information relating to this reportable segment. The terms “we,” “us,” “our” and “ours” are used to refer to DPL and its subsidiaries. DPL is an indirectly wholly-owned subsidiary of AES. DP&L , a wholly-owned subsidiary of DPL that does business as AES Ohio , is a public utility incorporated in 1911 under the laws of Ohio. Beginning in 2001, Ohio law gave Ohio consumers the right to choose the electric generation supplier from whom they purchase retail generation service; however, retail transmission and distribution services are still regulated. AES Ohio has the exclusive right to provide such transmission and distribution services to approximately 533,000 customers located in West Central Ohio. Additionally, AES Ohio provides retail SSO electric service to residential, commercial, industrial and governmental customers in a 6,000-square mile area of West Central Ohio. AES Ohio sources all of the generation for its SSO customers through a competitive bid process. Principal industries located in AES Ohio’s service territory include automotive, food processing, paper, plastic, manufacturing and defense. AES Ohio's sales reflect the general economic conditions, seasonal weather patterns of the area, the market price of electricity and customer energy efficiency initiatives. AES Ohio owned interests in the retired Hutchings Coal Station until its transfer in 2020 and currently owns numerous transmission facilities. AES Ohio sells its proportional share of energy and capacity from its investment in OVEC into the wholesale market. DPL’s other primary subsidiaries are MVIC and Miami Valley Lighting. MVIC is our captive insurance company that provides insurance services to AES Ohio and our other subsidiaries, and Miami Valley Lighting provides street and outdoor lighting services to customers in the Dayton region. In prior periods, AES Ohio Generation was also a primary subsidiary and sold all of its energy and capacity into the wholesale market. AES Ohio Generation retired its only remaining operating asset in May 2020 and sold it in June 2020. See Note 12 – Discontinued Operations for more information. DPL's subsidiaries are all wholly-owned. DPL also has a wholly-owned business trust, DPL Capital Trust II, formed for the purpose of issuing trust capital securities to investors. AES Ohio’s electric transmission and distribution businesses are subject to rate regulation by federal and state regulators. Accordingly, AES Ohio applies the accounting standards for regulated operations to its electric transmission and distribution businesses and records regulatory assets when incurred costs are expected to be recovered in future customer rates and regulatory liabilities when current cost recoveries in customer rates relate to expected future costs or overcollections of riders.
Financial Statement Presentation	Financial Statement Presentation DPL’s Condensed Consolidated Financial Statements include the accounts of DPL and its wholly-owned subsidiaries except for DPL Capital Trust II, which is not consolidated, consistent with the provisions of GAAP. Certain immaterial amounts from prior periods have been reclassified to conform to the current period presentation. All material intercompany accounts and transactions are eliminated in consolidation. We have evaluated subsequent events through the date this report is issued. These financial statements have been prepared in accordance with GAAP, as contained in the FASB ASC, for interim financial statements and Article 10 of Regulation S-X issued by the SEC. Accordingly, they do not include all the information and footnotes required by GAAP for annual fiscal reporting periods. Therefore, our interim financial statements in this report should be read along with the annual financial statements included in our Form 10-K for the fiscal year ended December 31, 2020. In the opinion of our management, the Condensed Consolidated Financial Statements presented in this report contain all adjustments necessary to fairly state our financial position as of September 30, 2021; our results of operations for the three and nine months ended September 30, 2021 and 2020, our cash flows for the nine months ended September 30, 2021 and 2020 and the changes in our equity for the three and nine months ended September 30, 2021 and 2020. Unless otherwise noted, all adjustments are normal and recurring in nature. Due to various factors, interim results for the three and nine months ended September 30, 2021 may not be indicative of our results that will be realized for the full year ending December 31, 2021. The preparation of financial statements in conformity with GAAP requires us to make estimates and judgments that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities, and the revenues and expenses of the periods reported. Actual results could differ from these estimates. Significant items subject to such estimates and judgments include: recognition of revenue including unbilled revenues, the carrying value of property, plant and equipment; the valuation of insurance and claims liabilities; the valuation of allowances for credit losses and deferred income taxes; regulatory assets and liabilities; liabilities recorded for income tax exposures; litigation; contingencies; and assets and liabilities related to employee benefits.
Accounting for Taxes Collected from Customers and Remitted to Governmental Authorities	AES Ohio collects certain excise taxes levied by state or local governments from its customers. These taxes are accounted for on a net basis and not included in revenue. The amounts of such taxes collected for the three and nine months ended September 30, 2021 and 2020 were as follows: Three months ended Nine months ended September 30, September 30, $ in millions 2021 2020 2021 2020 Excise taxes collected $ 13.5 $ 13.4 $ 37.7 $ 36.7
Recently Issued Accounting Standards	New Accounting Pronouncements Adopted in 2021 – We have assessed and determined that the new accounting pronouncements adopted did not have a material impact on our consolidated financial statements. New Accounting Pronouncements Issued But Not Yet Effective – The following table provides a brief description of recent accounting pronouncements that could have a material impact on our consolidated financial statements. Accounting pronouncements not listed below were assessed and determined to be either not applicable or are expected to have no material impact on our consolidated financial statements. ASU Number and Name Description Date of Adoption Effect on the financial statements upon adoption 2020-04, Reference Rate Form (Topic 848): Facilitation of the Effects of Reference Rate Reform on Financial Reporting The standard provides optional expedients and exceptions for applying GAAP to contracts, hedging relationships and other transactions that reference to LIBOR or another reference rate expected to be discontinued by reference rate reform. This standard is effective for a limited period of time (March 12, 2020 - December 21, 2022). Effective for all entities March 12, 2020 - December 31, 2022 We are currently evaluating the impact of adopting the standard on our condensed consolidated financial statements.
Inventory, Policy	Inventories Inventories consist of materials and supplies as of September 30, 2021 and December 31, 2020.
Subsidiaries [Member]
Significant Accounting Policies [Line Items]
Description of Business	Description of Business DP&L , which does business as AES Ohio , is a public utility incorporated in 1911 under the laws of Ohio. Beginning in 2001, Ohio law gave Ohio consumers the right to choose the electric generation supplier from whom they purchase retail generation service; however, retail transmission and distribution services are still regulated. AES Ohio has the exclusive right to provide such transmission and distribution services to approximately 533,000 customers located in West Central Ohio. Additionally, AES Ohio provides retail SSO electric service to residential, commercial, industrial and governmental customers in a 6,000-square mile area of West Central Ohio. AES Ohio sources all of the generation for its SSO customers through a competitive bid process. Principal industries located in AES Ohio’s service territory include automotive, food processing, paper, plastic, manufacturing and defense. AES Ohio's sales reflect the general economic conditions, seasonal weather patterns of the area, the market price of electricity and customer energy efficiency initiatives. AES Ohio owned interests in the retired Hutchings Coal Station until its transfer in 2020 and currently owns numerous transmission facilities. AES Ohio sells its proportional share of energy and capacity from its investment in OVEC into the wholesale market. AES Ohio has one reportable segment, the Utility segment. In addition to AES Ohio's electric transmission and distribution businesses, the Utility segment includes revenues and costs associated with AES Ohio's investment in OVEC and the historical results of AES Ohio’s Hutchings Coal Station. AES Ohio is a subsidiary of DPL. The terms “we,” “us,” “our” and “ours” are used to refer to AES Ohio . AES Ohio’s electric transmission and distribution businesses are subject to rate regulation by federal and state regulators. Accordingly, AES Ohio applies the accounting standards for regulated operations to its electric transmission and distribution businesses and records regulatory assets when incurred costs are expected to be recovered in future customer rates and regulatory liabilities when current cost recoveries in customer rates relate to expected future costs or overcollections of riders.
Financial Statement Presentation	Financial Statement Presentation AES Ohio does not have any subsidiaries. We have evaluated subsequent events through the date this report is issued. Certain immaterial amounts from prior periods have been reclassified to conform to the current period presentation. These financial statements have been prepared in accordance with GAAP, as contained in the FASB ASC, for interim financial statements and Article 10 of Regulation S-X issued by the SEC. Accordingly, they do not include all the information and footnotes required by GAAP for annual fiscal reporting periods. Therefore, our interim financial statements in this report should be read along with the annual financial statements included in our Form 10-K for the fiscal year ended December 31, 2020. In the opinion of our management, the Condensed Financial Statements presented in this report contain all adjustments necessary to fairly state our financial position as of September 30, 2021; our results of operations for the three and nine months ended September 30, 2021 and 2020, our cash flows for the nine months ended September 30, 2021 and 2020 and the changes in our equity for the three and nine months ended September 30, 2021 and 2020. Unless otherwise noted, all adjustments are normal and recurring in nature. Due to various factors, interim results for the three and nine months ended September 30, 2021 may not be indicative of our results that will be realized for the full year ending December 31, 2021. The preparation of financial statements in conformity with GAAP requires us to make estimates and judgments that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities, and the revenues and expenses of the periods reported. Actual results could differ from these estimates. Significant items subject to such estimates and judgments include: recognition of revenue including unbilled revenues, the carrying value of property, plant and equipment; the valuation of insurance and claims liabilities; the valuation of allowances for credit losses and deferred income taxes; regulatory assets and liabilities; liabilities recorded for income tax exposures; litigation; contingencies; and assets and liabilities related to employee benefits.
Accounting for Taxes Collected from Customers and Remitted to Governmental Authorities	AES Ohio collects certain excise taxes levied by state or local governments from its customers. These taxes are accounted for on a net basis and not included in revenue. The amounts of such taxes collected for the three and nine months ended September 30, 2021 and 2020 were as follows: Three months ended Nine months ended September 30, September 30, $ in millions 2021 2020 2021 2020 Excise taxes collected $ 13.5 $ 13.4 $ 37.7 $ 36.7
Recently Issued Accounting Standards	New Accounting Pronouncements Adopted in 2021 – We have assessed and determined that the new accounting pronouncements adopted did not have a material impact on our financial statements. New Accounting Pronouncements Issued But Not Yet Effective – The following table provides a brief description of recent accounting pronouncements that could have a material impact on our financial statements. Accounting pronouncements not listed below were assessed and determined to be either not applicable or are expected to have no material impact on our financial statements. ASU Number and Name Description Date of Adoption Effect on the financial statements upon adoption 2020-04, Reference Rate Form (Topic 848): Facilitation of the Effects of Reference Rate Reform on Financial Reporting The standard provides optional expedients and exceptions for applying GAAP to contracts, hedging relationships and other transactions that reference to LIBOR or another reference rate expected to be discontinued by reference rate reform. This standard is effective for a limited period of time (March 12, 2020 - December 21, 2022). Effective for all entities March 12, 2020 - December 31, 2022 We are currently evaluating the impact of adopting the standard on our condensed financial statements.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Tables)	9 Months Ended
	Sep. 30, 2021
Related Party Transaction [Line Items]
Schedule of Accumulated Other Comprehensive Income (Loss)	The changes in the components of Accumulated other comprehensive loss during the nine months ended September 30, 2021 are as follows: $ in millions Gains / (losses) on cash flow hedges Change in unfunded pension and postretirement benefit obligations Total Balance as of January 1, 2021 $ 13.6 $ (25.9) $ (12.3) Amounts reclassified from AOCL to earnings (0.6) 1.5 0.9 Net current period other comprehensive income / (loss) (0.6) 1.5 0.9 Balance as of September 30, 2021 $ 13.0 $ (24.4) $ (11.4)
Reclassification out of Accumulated Other Comprehensive Income	The amounts reclassified out of Accumulated other comprehensive loss by component during the three and nine months ended September 30, 2021 and 2020 are as follows: Details about Accumulated Other Comprehensive Loss components Affected line item in the Condensed Consolidated Statements of Operations Three months ended Nine months ended September 30, September 30, $ in millions 2021 2020 2021 2020 Gains and losses on cash flow hedges (Note 4): Interest expense $ (0.2) $ (0.3) $ (0.7) $ (0.9) Income tax expense — — 0.1 0.1 Net of income taxes (0.2) (0.3) (0.6) (0.8) Amortization of defined benefit pension items (Note 7): Other expense 0.6 0.3 1.9 0.9 Income tax benefit (0.1) — (0.4) (0.1) Net of income taxes 0.5 0.3 1.5 0.8 Total reclassifications for the period, net of income taxes $ 0.3 $ — $ 0.9 $ —
Schedule of Supplemental Financial Information	Accounts receivable were as follows as of September 30, 2021 and December 31, 2020: September 30, December 31, $ in millions 2021 2020 Accounts receivable, net: Customer receivables $ 47.3 $ 48.5 Unbilled revenue 15.6 21.6 Amounts due from affiliates 1.5 0.2 Due from PJM transmission enhancement settlement 1.7 1.7 Other 3.1 0.5 Allowance for credit losses (0.9) (2.8) Total accounts receivable, net $ 68.3 $ 69.7
Accounts Receivable, Allowance for Credit Loss	The following table is a roll forward of our allowance for credit losses related to the accounts receivable balances for the nine months ended September 30, 2021 and 2020: $ in millions Beginning Allowance Balance Current Period Provision Write-offs Charged Against Allowances Recoveries Collected Ending Allowance Balance 2021 $ 2.8 $ (0.4) $ (2.6) $ 1.1 $ 0.9 2020 $ 0.4 $ 2.8 $ (1.4) $ 1.4 $ 3.2 The allowance for credit losses primarily relates to utility customer receivables, including unbilled amounts. Expected credit loss estimates are developed by disaggregating customers into those with similar credit risk characteristics and using historical credit loss experience. In addition, we also consider how current and future economic conditions are expected to impact collectability, as applicable, including the economic impacts of the COVID-19 pandemic on our receivable balance as of September 30, 2021. Amounts are written off when reasonable collections efforts have been exhausted. During 2021, the current period provision and allowance for credit losses have decreased due to lower past due customer receivable balances. See Note 13 – Risks and Uncertainties for additional discussion of the COVID-19 pandemic.
New Accounting Pronouncements, Policy [Policy Text Block]	New Accounting Pronouncements Adopted in 2021 – We have assessed and determined that the new accounting pronouncements adopted did not have a material impact on our consolidated financial statements. New Accounting Pronouncements Issued But Not Yet Effective – The following table provides a brief description of recent accounting pronouncements that could have a material impact on our consolidated financial statements. Accounting pronouncements not listed below were assessed and determined to be either not applicable or are expected to have no material impact on our consolidated financial statements. ASU Number and Name Description Date of Adoption Effect on the financial statements upon adoption 2020-04, Reference Rate Form (Topic 848): Facilitation of the Effects of Reference Rate Reform on Financial Reporting The standard provides optional expedients and exceptions for applying GAAP to contracts, hedging relationships and other transactions that reference to LIBOR or another reference rate expected to be discontinued by reference rate reform. This standard is effective for a limited period of time (March 12, 2020 - December 21, 2022). Effective for all entities March 12, 2020 - December 31, 2022 We are currently evaluating the impact of adopting the standard on our condensed consolidated financial statements.
Schedule of Cash and Cash Equivalents [Table Text Block]	The following table provides a summary of cash, cash equivalents, and restricted cash amounts reported on the Condensed Consolidated Balance Sheets that reconcile to the total of such amounts as shown on the Condensed Consolidated Statements of Cash Flows: $ in millions September 30, 2021 December 31, 2020 Cash and cash equivalents $ 41.5 $ 25.4 Restricted cash 0.1 0.1 Cash, Cash Equivalents, and Restricted Cash, End of Period $ 41.6 $ 25.5
Schedule of New Accounting Pronouncements	New Accounting Pronouncements Issued But Not Yet Effective – The following table provides a brief description of recent accounting pronouncements that could have a material impact on our consolidated financial statements. Accounting pronouncements not listed below were assessed and determined to be either not applicable or are expected to have no material impact on our consolidated financial statements. ASU Number and Name Description Date of Adoption Effect on the financial statements upon adoption 2020-04, Reference Rate Form (Topic 848): Facilitation of the Effects of Reference Rate Reform on Financial Reporting The standard provides optional expedients and exceptions for applying GAAP to contracts, hedging relationships and other transactions that reference to LIBOR or another reference rate expected to be discontinued by reference rate reform. This standard is effective for a limited period of time (March 12, 2020 - December 21, 2022). Effective for all entities March 12, 2020 - December 31, 2022 We are currently evaluating the impact of adopting the standard on our condensed consolidated financial statements.
Subsidiaries [Member]
Related Party Transaction [Line Items]
Schedule of Accumulated Other Comprehensive Income (Loss)	The changes in the components of Accumulated other comprehensive loss during the nine months ended September 30, 2021 are as follows: $ in millions Change in Accumulated other comprehensive loss Balance as of January 1, 2021 $ (42.1) Amounts reclassified from AOCL to earnings 2.9 Net current period other comprehensive income 2.9 Balance as of September 30, 2021 $ (39.2)
Reclassification out of Accumulated Other Comprehensive Income	The amounts reclassified out of Accumulated other comprehensive loss by component during the three and nine months ended September 30, 2021 and 2020 are as follows: Details about Accumulated Other Comprehensive Loss components Affected line item in the Condensed Consolidated Statements of Operations Three months ended Nine months ended September 30, September 30, $ in millions 2021 2020 2021 2020 Gains and losses on cash flow hedges (Note 4): Interest expense $ — $ — $ — $ (0.2) Income tax benefit — (0.1) — (0.1) Net of income taxes — (0.1) — (0.3) Amortization of defined benefit pension items (Note 7): Other expense 1.3 1.0 3.8 3.0 Income tax benefit (0.3) (0.2) (0.9) (0.6) Net of income taxes 1.0 0.8 2.9 2.4 Total reclassifications for the period, net of income taxes $ 1.0 $ 0.7 $ 2.9 $ 2.1
Schedule of Supplemental Financial Information	Accounts receivable were as follows as of September 30, 2021 and December 31, 2020: September 30, December 31, $ in millions 2021 2020 Accounts receivable, net: Customer receivables 46.6 $ 47.6 Unbilled revenue 15.6 21.6 Amounts due from affiliates 2.3 1.9 Due from PJM transmission enhancement settlement 1.7 1.7 Other 3.2 0.2 Allowance for credit losses (0.9) (2.8) Total accounts receivable, net $ 68.5 $ 70.2
Accounts Receivable, Allowance for Credit Loss	The following table is a roll forward of our allowance for credit losses related to the accounts receivable balances for the nine months ended September 30, 2021 and 2020: $ in millions Beginning Allowance Balance Current Period Provision Write-offs Charged Against Allowances Recoveries Collected Ending Allowance Balance 2021 $ 2.8 $ (0.4) $ (2.6) $ 1.1 $ 0.9 2020 $ 0.4 $ 2.8 $ (1.4) $ 1.4 $ 3.2
New Accounting Pronouncements, Policy [Policy Text Block]	New Accounting Pronouncements Adopted in 2021 – We have assessed and determined that the new accounting pronouncements adopted did not have a material impact on our financial statements. New Accounting Pronouncements Issued But Not Yet Effective – The following table provides a brief description of recent accounting pronouncements that could have a material impact on our financial statements. Accounting pronouncements not listed below were assessed and determined to be either not applicable or are expected to have no material impact on our financial statements. ASU Number and Name Description Date of Adoption Effect on the financial statements upon adoption 2020-04, Reference Rate Form (Topic 848): Facilitation of the Effects of Reference Rate Reform on Financial Reporting The standard provides optional expedients and exceptions for applying GAAP to contracts, hedging relationships and other transactions that reference to LIBOR or another reference rate expected to be discontinued by reference rate reform. This standard is effective for a limited period of time (March 12, 2020 - December 21, 2022). Effective for all entities March 12, 2020 - December 31, 2022 We are currently evaluating the impact of adopting the standard on our condensed financial statements.
Schedule of Cash and Cash Equivalents [Table Text Block]	The following table provides a summary of cash, cash equivalents, and restricted cash amounts reported on the Condensed Balance Sheets that reconcile to the total of such amounts as shown on the Condensed Statements of Cash Flows: $ in millions September 30, 2021 December 31, 2020 Cash and cash equivalents $ 29.8 $ 11.7 Restricted cash 0.1 0.1 Cash, Cash Equivalents, and Restricted Cash, End of Period $ 29.9 $ 11.8

Fair Value (Tables)

Fair Value (Tables)	9 Months Ended
	Sep. 30, 2021
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value and Cost Of Non-Derivative Instruments	The following table presents the fair value, carrying value and cost of our non-derivative instruments as of September 30, 2021 and December 31, 2020. Further information about the fair value of our derivative instruments can be found in Note 4 – Derivative Instruments and Hedging Activities. September 30, 2021 December 31, 2020 $ in millions Cost Fair Value Cost Fair Value Assets Money market funds $ 0.4 $ 0.4 $ 0.3 $ 0.3 Equity securities 2.0 4.9 2.1 4.5 Debt securities 3.8 3.8 4.0 4.1 Total $ 6.2 $ 9.1 $ 6.4 $ 8.9 Carrying Value Fair Value Carrying Value Fair Value Liabilities Long-term debt $ 1,395.1 $ 1,534.0 $ 1,393.6 $ 1,571.6
Fair Value of Assets and Liabilities Measured on Recurring Basis	The fair value of assets and liabilities as of September 30, 2021 and December 31, 2020 and the respective category within the fair value hierarchy for DPL is as follows: $ in millions Fair value as of September 30, 2021 (a) Fair value as of December 31, 2020 (a) Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Assets Master Trust assets Money market funds $ 0.4 $ — $ — $ 0.4 $ 0.3 $ — $ — $ 0.3 Equity securities — 4.9 — 4.9 — 4.5 — 4.5 Debt securities — 3.8 — 3.8 — 4.1 — 4.1 Total Master Trust assets 0.4 8.7 — 9.1 0.3 8.6 — 8.9 Total $ 0.4 $ 8.7 $ — $ 9.1 $ 0.3 $ 8.6 $ — $ 8.9 Liabilities Long-term debt $ — $ 1,516.8 $ 17.2 $ 1,534.0 $ — $ 1,554.2 $ 17.4 $ 1,571.6 Total Liabilities $ — $ 1,516.8 $ 17.2 $ 1,534.0 $ — $ 1,554.2 $ 17.4 $ 1,571.6 (a) Includes credit valuation adjustment
Subsidiaries [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value and Cost Of Non-Derivative Instruments	The following table presents the fair value, carrying value and cost of our non-derivative instruments as of September 30, 2021 and December 31, 2020. Further information about the fair value of our derivative instruments can be found in Note 4 – Derivative Instruments and Hedging Activities. September 30, 2021 December 31, 2020 $ in millions Cost Fair Value Cost Fair Value Assets Money market funds $ 0.4 $ 0.4 $ 0.3 $ 0.3 Equity securities 2.0 4.9 2.1 4.5 Debt securities 3.8 3.8 4.0 4.1 Total $ 6.2 $ 9.1 $ 6.4 $ 8.9 Carrying Value Fair Value Carrying Value Fair Value Liabilities Long-term debt $ 574.2 $ 635.5 $ 574.1 $ 656.0
Fair Value of Assets and Liabilities Measured on Recurring Basis	The fair value of assets and liabilities as of September 30, 2021 and December 31, 2020 and the respective category within the fair value hierarchy for AES Ohio is as follows: $ in millions Fair value as of September 30, 2021 (a) Fair value as of December 31, 2020 (a) Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Assets Master Trust assets Money market funds $ 0.4 $ — $ — $ 0.4 $ 0.3 $ — $ — $ 0.3 Equity securities — 4.9 — 4.9 — 4.5 — 4.5 Debt securities — 3.8 — 3.8 — 4.1 — 4.1 Total $ 0.4 $ 8.7 $ — $ 9.1 $ 0.3 $ 8.6 $ — $ 8.9 Liabilities Long-term debt $ — $ 618.3 $ 17.2 $ 635.5 $ — $ 638.6 $ 17.4 $ 656.0 Total Liabilities $ — $ 618.3 $ 17.2 $ 635.5 $ — $ 638.6 $ 17.4 $ 656.0 (a) Includes credit valuation adjustment

Derivative Instruments and He_2

Derivative Instruments and Hedging Activities (Tables)	9 Months Ended
	Sep. 30, 2021
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gains or Losses Recognized in AOCI for the Cash Flow Hedges	The following tables provide information concerning gains or losses recognized in AOCL for the cash flow hedges for the three and nine months ended September 30, 2021 and 2020: Three months ended Nine months ended September 30, 2021 September 30, 2020 September 30, 2021 September 30, 2020 Interest Interest Interest Interest $ in millions (net of tax) Rate Hedge Rate Hedge Rate Hedge Rate Hedge Beginning accumulated derivative gains in AOCL $ 13.2 $ 13.9 $ 13.6 $ 14.5 Net gains associated with current period hedging transactions — 0.1 — — Net gains reclassified to earnings Interest expense (0.2) (0.3) (0.6) (0.8) Ending accumulated derivative gains in AOCL $ 13.0 $ 13.7 $ 13.0 $ 13.7 Portion expected to be reclassified to earnings in the next twelve months $ (0.8)
Subsidiaries [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gains or Losses Recognized in AOCI for the Cash Flow Hedges	The following tables provide information concerning gains or losses recognized in AOCL for the cash flow hedges for the three and nine months ended September 30, 2020: Three months ended Nine months ended September 30, 2020 September 30, 2020 Interest Interest $ in millions (net of tax) Rate Hedge Rate Hedge Beginning accumulated derivative losses in AOCL $ (0.7) $ (0.4) Net gains associated with current period hedging transactions 0.2 0.1 Net gains reclassified to earnings Interest expense (0.1) (0.3) Ending accumulated derivative losses in AOCL $ (0.6) $ (0.6)

Debt (Tables)

Debt (Tables)	9 Months Ended
	Sep. 30, 2021
Debt Instrument [Line Items]
Long-term Debt	Long-term Debt Long-term debt is as follows: Interest September 30, December 31, $ in millions Rate Maturity 2021 2020 First Mortgage Bonds 3.95% 2049 $ 425.0 $ 425.0 First Mortgage Bonds 3.20% 2040 140.0 140.0 U.S. Government note 4.20% 2061 17.2 17.4 Unamortized deferred financing costs (5.5) (5.7) Unamortized debt discounts, net (2.5) (2.6) Total long-term debt at AES Ohio 574.2 574.1 Senior unsecured bonds 4.125% 2025 415.0 415.0 Senior unsecured bonds 4.35% 2029 400.0 400.0 Note to DPL Capital Trust II (a) 8.125% 2031 15.6 15.6 Unamortized deferred financing costs (8.8) (10.2) Unamortized debt discounts, net (0.9) (0.9) Total long-term debt 1,395.1 1,393.6 Less: current portion (0.2) (0.2) Long-term debt, net of current portion $ 1,394.9 $ 1,393.4 (a) Note payable to related party. Lines of credit As of September 30, 2021 and December 31, 2020, the DPL Credit Agreement had outstanding borrowings of $80.0 million and $80.0 million, respectively. As of September 30, 2021 and December 31, 2020, the AES Ohio Credit Agreement had outstanding borrowings of $140.0 million and $20.0 million, respectively. Significant transactions On July 31, 2020, AES Ohio issued $140.0 million of taxable First Mortgage Bonds and on August 3, 2020 used the proceeds to purchase at par value the $140.0 million of outstanding tax-exempt Ohio Air Quality Development Authority (OAQDA) Collateralized Pollution Control Revenue Refunding Bonds that had been issued in 2015. The new taxable First Mortgage Bonds carry an interest rate of 3.20% and mature on July 31, 2040. The OAQDA Revenue bonds have not been legally cancelled and can be re-issued at the discretion of AES Ohio at any time. These bonds will be held in trust while we continue to evaluate market conditions and explore suitable long-term financing alternatives. Accordingly, as of September 30, 2021 and December 31, 2020, the $140.0 million variable rate OAQDA Revenue bonds are not treated as being outstanding in the Condensed Consolidated Balance Sheet. On June 19, 2020, DPL closed a $415.0 million issuance of senior unsecured notes. These notes carry an interest rate of 4.125% and mature on July 1, 2025. Proceeds from the issuance and cash on hand were used to redeem in-full the remaining balance of $380.0 million of DPL's 7.25% senior unsecured notes. These bonds were redeemed at par plus accrued interest and a make-whole premium of $30.8 million on July 20, 2020. DPL agreed to register the 2025 DPL Senior Unsecured Bonds under the Securities Act by filing an exchange offer registration statement or, under specified circumstances, a shelf registration statement with the SEC pursuant to a Registration Rights Agreement dated June 19, 2020. DPL filed a registration statement on Form S-4 with respect to the 2025 DPL Senior Unsecured Bonds with the SEC on March 15, 2021, and this registration statement was declared effective on March 31, 2021. The exchange offer closed on May 5, 2021. On June 1, 2020, the DPL Credit Agreement was amended. As a result of the amendment, the borrowing limit was reduced from $125.0 million to $110.0 million, the Total Debt to EBITDA covenant was eliminated, the EBITDA to Interest Expense covenant was reduced from 2.25 to 1.00 to 1.70 to 1.00, increasing to 1.75 to 1.00 as of September 30, 2022 and 2.00 to 1.00 as of December 31, 2022, and a trailing-twelve months minimum EBITDA covenant of $125.0 million was added, increasing to $130.0 million as of September 30, 2022 and $150.0 million as of December 31, 2022. Starting with the quarter ended September 30, 2021, the borrowing limit will be reduced by $5.0 million per quarter should DPL’s Total Debt to EBITDA ratio calculated for the period of four consecutive quarters exceed 7.00 to 1.00. Long-term debt covenants and restrictions The DPL Credit Agreement has two financial covenants. The first financial covenant, a minimum EBITDA, calculated at the end of each fiscal quarter for the four prior fiscal quarters, of $125.0 million is required, stepping up to $130.0 million on September 30, 2022 and $150.0 million on December 31, 2022. As of September 30, 2021, DPL was in compliance with this financial covenant. The second financial covenant is an EBITDA to Interest Expense ratio that is calculated, at the end of each fiscal quarter, by dividing EBITDA for the four prior fiscal quarters by the consolidated interest charges for the same period. The ratio, per the agreement, is to be not less than 1.70 to 1.00, and steps up to 1.75 to 1.00 on September 30, 2022 and 2.00 to 1.00 as of December 31, 2022. As of September 30, 2021, DPL was in compliance with this financial covenant. The DPL Credit Agreement also restricts dividend payments from DPL to AES, such that DPL cannot make dividend payments unless at the time of, and/or as a result of the distribution, (i) DPL’s leverage ratio does not exceed 0.67 to 1.00 and DPL’s interest coverage ratio is not less than 2.50 to 1.00 or, if such ratios are not within the parameters, (ii) DPL’s senior long-term debt rating from two of the three major credit rating agencies is at least investment grade. As a result, as of September 30, 2021, DPL was prohibited from making a distribution to its shareholder or making a loan to any of its affiliates (other than its subsidiaries). Starting with the quarter ended September 30, 2021, the borrowing limit on the DPL Credit Agreement will be reduced by $5.0 million per quarter should the Total Debt to EBITDA ratio for the period of four consecutive quarters exceed 7.00 to 1.00. As of September 30, 2021, DPL exceeded this ratio and the borrowing limit was reduced from $110.0 million to $105.0 million. The AES Ohio Credit Agreement and Bond Purchase Agreement (financing document entered into in connection with the issuance of AES Ohio's First Mortgage Bonds, on July 31, 2020) has one financial covenant. The covenant measures Total Debt to Total Capitalization and is calculated, at the end of each fiscal quarter, by dividing total debt at the end of the quarter by total capitalization at the end of the quarter. AES Ohio’s Total Debt to Total Capitalization ratio shall not be greater than 0.67 to 1.00. As of September 30, 2021, AES Ohio was in compliance with this financial covenant. As of September 30, 2021, DPL and AES Ohio were in compliance with all debt covenants, including the financial covenants described above. AES Ohio does not have any meaningful restrictions in its debt financing documents prohibiting dividends and return of capital payments to its parent, DPL. Substantially all property, plant & equipment of AES Ohio is subject to the lien of the mortgage securing AES Ohio’s First and Refunding Mortgage.
Schedule of Long-term Debt Instruments	Long-term debt is as follows: Interest September 30, December 31, $ in millions Rate Maturity 2021 2020 First Mortgage Bonds 3.95% 2049 $ 425.0 $ 425.0 First Mortgage Bonds 3.20% 2040 140.0 140.0 U.S. Government note 4.20% 2061 17.2 17.4 Unamortized deferred financing costs (5.5) (5.7) Unamortized debt discounts, net (2.5) (2.6) Total long-term debt at AES Ohio 574.2 574.1 Senior unsecured bonds 4.125% 2025 415.0 415.0 Senior unsecured bonds 4.35% 2029 400.0 400.0 Note to DPL Capital Trust II (a) 8.125% 2031 15.6 15.6 Unamortized deferred financing costs (8.8) (10.2) Unamortized debt discounts, net (0.9) (0.9) Total long-term debt 1,395.1 1,393.6 Less: current portion (0.2) (0.2) Long-term debt, net of current portion $ 1,394.9 $ 1,393.4 (a) Note payable to related party.
Subsidiaries [Member]
Debt Instrument [Line Items]
Long-term Debt	Long-term Debt Long-term debt is as follows: Interest September 30, December 31, $ in millions Rate Maturity 2021 2020 First Mortgage Bonds 3.95 % 2049 $ 425.0 $ 425.0 First Mortgage Bonds 3.20 % 2040 140.0 140.0 U.S. Government note 4.20 % 2061 17.2 17.4 Unamortized deferred financing costs (5.5) (5.7) Unamortized debt discounts, net (2.5) (2.6) Total long-term debt 574.2 574.1 Less: current portion (0.2) (0.2) Long-term debt, net of current portion $ 574.0 $ 573.9 Line of credit As of September 30, 2021 and December 31, 2020, the AES Ohio Credit Agreement had outstanding borrowings on its line of credit of $140.0 million and $20.0 million, respectively. Significant transactions On July 31, 2020, AES Ohio issued $140.0 million of taxable First Mortgage Bonds and on August 3, 2020 used the proceeds to purchase at par value the $140.0 million of outstanding tax-exempt Ohio Air Quality Development Authority (OAQDA) Collateralized Pollution Control Revenue Refunding Bonds that had been issued in 2015. The new taxable First Mortgage Bonds carry an interest rate of 3.20% and mature on July 31, 2040. The OAQDA Revenue bonds have not been legally cancelled and can be re-issued at the discretion of AES Ohio at any time. These bonds will be held in trust while we continue to evaluate market conditions and explore suitable long-term financing alternatives. Accordingly, as of September 30, 2021 and December 31, 2020, the $140.0 million variable rate OAQDA Revenue bonds are not treated as being outstanding in the Condensed Consolidated Balance Sheet. Long-term debt covenants and restrictions The AES Ohio Credit Agreement and Bond Purchase Agreement (financing document entered into in connection with the issuance of AES Ohio's First Mortgage Bonds, on July 31, 2020) has one financial covenant. The covenant measures Total Debt to Total Capitalization and is calculated, at the end of each fiscal quarter, by dividing total debt at the end of the quarter by total capitalization at the end of the quarter. AES Ohio’s Total Debt to Total Capitalization ratio shall not be greater than 0.67 to 1.00. As of September 30, 2021, AES Ohio was in compliance with this financial covenant. As of September 30, 2021, AES Ohio was in compliance with all debt covenants, including the financial covenants described above. AES Ohio does not have any meaningful restrictions in its debt financing documents prohibiting dividends and return of capital payments to its parent, DPL. Substantially all property, plant & equipment of AES Ohio is subject to the lien of the mortgage securing AES Ohio’s First and Refunding Mortgage.
Schedule of Long-term Debt Instruments	Long-term debt is as follows: Interest September 30, December 31, $ in millions Rate Maturity 2021 2020 First Mortgage Bonds 3.95 % 2049 $ 425.0 $ 425.0 First Mortgage Bonds 3.20 % 2040 140.0 140.0 U.S. Government note 4.20 % 2061 17.2 17.4 Unamortized deferred financing costs (5.5) (5.7) Unamortized debt discounts, net (2.5) (2.6) Total long-term debt 574.2 574.1 Less: current portion (0.2) (0.2) Long-term debt, net of current portion $ 574.0 $ 573.9

Benefit Plans (Tables)

Benefit Plans (Tables)	9 Months Ended
	Sep. 30, 2021
Entity Information [Line Items]
Schedule of Net Periodic Benefit Cost / (Income)	The net periodic benefit cost of the pension benefit plans for the three and nine months ended September 30, 2021 and 2020 was: Three months ended Nine months ended September 30, September 30, $ in millions 2021 2020 2021 2020 Service cost $ 1.2 $ 0.9 $ 3.4 $ 2.8 Interest cost 2.1 2.9 6.1 8.8 Expected return on plan assets (3.8) (4.6) (11.2) (14.0) Amortization of unrecognized: Prior service cost 0.2 0.3 0.6 0.8 Actuarial loss 2.2 1.5 6.8 4.6 Net periodic benefit cost $ 1.9 $ 1.0 $ 5.7 $ 3.0
Subsidiaries [Member]
Entity Information [Line Items]
Schedule of Net Periodic Benefit Cost / (Income)	The net periodic benefit cost of the pension benefit plans for the three and nine months ended September 30, 2021 and 2020 was: Three months ended Nine months ended September 30, September 30, $ in millions 2021 2020 2021 2020 Service cost $ 1.2 $ 0.9 $ 3.4 $ 2.8 Interest cost 2.1 2.9 6.1 8.8 Expected return on plan assets (3.8) (4.6) (11.2) (14.0) Amortization of unrecognized: Prior service cost 0.2 0.3 0.8 1.0 Actuarial loss 2.9 2.2 8.5 6.5 Net periodic benefit cost $ 2.6 $ 1.7 $ 7.6 $ 5.1

Business Segments (Tables)

Business Segments (Tables)	9 Months Ended
	Sep. 30, 2021
Segment Reporting Information [Line Items]
Financial Reporting for Reportable Business Segments	The following tables present financial information for DPL’s Utility reportable business segment: $ in millions Utility Other Adjustments and Eliminations DPL Consolidated Three months ended September 30, 2021 Revenues from external customers $ 185.9 $ 2.3 $ — $ 188.2 Intersegment revenues 0.2 0.8 (1.0) — Total revenues $ 186.1 $ 3.1 $ (1.0) $ 188.2 Depreciation and amortization $ 18.6 $ 0.3 $ — $ 18.9 Interest expense $ 6.1 $ 9.7 $ — $ 15.8 Income / (loss) from continuing operations before income tax $ 16.1 $ (8.4) $ — $ 7.7 $ in millions Utility Other Adjustments and Eliminations DPL Consolidated Three Months Ended September 30, 2020 Revenues from external customers $ 176.8 $ 2.0 $ — $ 178.8 Intersegment revenues 0.2 1.0 (1.2) — Total revenues $ 177.0 $ 3.0 $ (1.2) $ 178.8 Depreciation and amortization $ 18.2 $ 0.4 $ — $ 18.6 Interest expense $ 5.9 $ 11.2 $ — $ 17.1 Loss on early extinguishment of debt $ — $ 31.7 $ — $ 31.7 Income / (loss) from continuing operations before income tax $ 21.3 $ (41.0) $ — $ (19.7) $ in millions Utility Other Adjustments and Eliminations DPL Consolidated Nine months ended September 30, 2021 Revenues from external customers $ 504.2 $ 7.3 $ 511.5 Intersegment revenues 0.6 2.6 (3.2) — Total revenues $ 504.8 $ 9.9 $ (3.2) $ 511.5 Depreciation and amortization $ 55.8 $ 1.1 $ — $ 56.9 Interest expense $ 18.1 $ 28.9 $ — $ 47.0 Income / (loss) from continuing operations before income tax $ 46.7 $ (23.6) $ — $ 23.1 $ in millions Utility Other Adjustments and Eliminations DPL Consolidated Nine months ended September 30, 2020 Revenues from external customers $ 498.4 $ 6.7 $ — $ 505.1 Intersegment revenues 0.7 2.7 (3.4) — Total revenues $ 499.1 $ 9.4 $ (3.4) $ 505.1 Depreciation and amortization $ 53.7 $ 1.1 $ — $ 54.8 Interest expense $ 18.5 $ 36.9 $ — $ 55.4 Loss on early extinguishment of debt $ — $ 31.7 $ — $ 31.7 Income / (loss) from continuing operations before income tax $ 49.7 $ (63.3) $ — $ (13.6) Total Assets September 30, 2021 December 31, 2020 Utility $ 2,067.6 $ 2,014.7 All Other (a) 21.1 21.3 DPL Consolidated $ 2,088.7 $ 2,036.0

Revenue (Tables)

Revenue (Tables)	9 Months Ended
	Sep. 30, 2021
Disaggregation of Revenue [Table Text Block]	The following table presents our revenue from contracts with customers and other revenue by segment for the three and nine months ended September 30, 2021 and 2020: $ in millions Utility Other Adjustments and Eliminations Total Three Months Ended September 30, 2021 Retail revenue Retail revenue from contracts with customers Residential revenue $ 103.3 $ — $ — $ 103.3 Commercial revenue 35.0 — — 35.0 Industrial revenue 16.0 — — 16.0 Governmental revenue 7.0 — — 7.0 Other (a) 2.9 — — 2.9 Total retail revenue from contracts with customers 164.2 — — 164.2 Wholesale revenue Wholesale revenue from contracts with customers 6.8 — (0.2) 6.6 RTO ancillary revenue 12.5 — — 12.5 Capacity revenue 1.8 — — 1.8 Miscellaneous revenue Miscellaneous revenue from contracts with customers (c) — 2.4 — 2.4 Other miscellaneous revenue 0.8 0.7 (0.8) 0.7 Total revenues $ 186.1 $ 3.1 $ (1.0) $ 188.2 $ in millions Utility Other Adjustments and Eliminations Total Three Months Ended September 30, 2020 Retail revenue Retail revenue from contracts with customers Residential revenue $ 99.3 $ — $ — $ 99.3 Commercial revenue 32.2 — — 32.2 Industrial revenue 14.5 — — 14.5 Governmental revenue 9.9 — — 9.9 Other (a) 3.7 — — 3.7 Total retail revenue from contracts with customers 159.6 — — 159.6 Other retail revenue (b) 0.1 — — 0.1 Wholesale revenue Wholesale revenue from contracts with customers 3.2 — (0.2) 3.0 RTO ancillary revenue 11.5 (0.1) — 11.4 Capacity revenue 0.9 — — 0.9 Miscellaneous revenue Miscellaneous revenue from contracts with customers (c) — 2.1 — 2.1 Other miscellaneous revenue 1.7 1.0 (1.0) 1.7 Total revenues $ 177.0 $ 3.0 $ (1.2) $ 178.8 Nine months ended September 30, 2021 Retail revenue Retail revenue from contracts with customers Residential revenue $ 279.3 $ — $ — $ 279.3 Commercial revenue 90.5 — — 90.5 Industrial revenue 42.4 — — 42.4 Governmental revenue 19.9 — — 19.9 Other (a) 9.4 — — 9.4 Total retail revenue from contracts with customers 441.5 — — 441.5 Wholesale revenue Wholesale revenue from contracts with customers 15.4 — (0.6) 14.8 RTO ancillary revenue 39.4 0.1 — 39.5 Capacity revenue 4.0 — — 4.0 Miscellaneous revenue Miscellaneous revenue from contracts with customers (c) — 7.2 — 7.2 Other miscellaneous revenue 4.5 2.6 (2.6) 4.5 Total revenues $ 504.8 $ 9.9 $ (3.2) $ 511.5 Nine months ended September 30, 2020 Retail revenue Retail revenue from contracts with customers Residential revenue $ 279.9 $ — $ — $ 279.9 Commercial revenue 87.6 — — 87.6 Industrial revenue 38.2 — — 38.2 Governmental revenue 27.7 — — 27.7 Other (a) 9.7 — — 9.7 Total retail revenue from contracts with customers 443.1 — — 443.1 Other retail revenue (b) 8.8 — — 8.8 Wholesale revenue Wholesale revenue from contracts with customers 7.7 — (0.7) 7.0 RTO ancillary revenue 32.3 — — 32.3 Capacity revenue 3.2 — — 3.2 Miscellaneous revenue Miscellaneous revenue from contracts with customers (c) — 6.7 — 6.7 Other miscellaneous revenue 4.0 2.7 (2.7) 4.0 Total revenues $ 499.1 $ 9.4 $ (3.4) $ 505.1 (a) "Other" primarily includes Wright-Patterson Air Force Base revenues, billing service fees from CRES providers and other miscellaneous retail revenues from contracts with customers. (b) Other retail revenue includes alternative revenue programs not accounted for under FASC 606. (c) Miscellaneous revenue from contracts with customers primarily includes revenues for various services provided by Miami Valley Lighting.
Subsidiaries [Member]
Disaggregation of Revenue [Table Text Block]	The following table presents our revenue from contracts with customers and other revenue for the three and nine months ended September 30, 2021 and 2020: Three months ended Nine months ended September 30, September 30, $ in millions 2021 2020 2021 2020 Retail revenue Retail revenue from contracts with customers Residential revenue $ 103.3 $ 99.3 $ 279.3 $ 279.9 Commercial revenue 35.0 32.2 90.5 87.6 Industrial revenue 16.0 14.5 42.4 38.2 Governmental revenue 7.0 9.9 19.9 27.7 Other (a) 2.9 3.7 9.4 9.7 Total retail revenue from contracts with customers 164.2 159.6 441.5 443.1 Other retail revenue (b) — 0.1 — 8.8 Wholesale revenue Wholesale revenue from contracts with customers 6.8 3.2 15.4 7.7 RTO ancillary revenue 12.5 11.5 39.4 32.3 Capacity revenue 1.8 0.9 4.0 3.2 Miscellaneous revenue 0.8 1.7 4.5 4.0 Total revenues $ 186.1 $ 177.0 $ 504.8 $ 499.1 (a) "Other" primarily includes Wright-Patterson Air Force Base revenues, billing service fees from CRES providers and other miscellaneous retail revenues from contracts with customers. (b) Other retail revenue includes alternative revenue programs not accounted for under FASC 606.

Discontinued Operations (Tables

Discontinued Operations (Tables)	9 Months Ended
	Sep. 30, 2021
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Disposal Groups, Including Discontinued Operations [Table Text Block]	The following table summarizes the revenues, operating costs, other expenses and income tax of discontinued operations for the periods indicated: Three months ended Nine months ended September 30, September 30, $ in millions 2021 2020 2021 2020 Revenues $ — $ 0.9 $ 1.4 $ 23.3 Operating costs and other expenses — 0.5 (2.4) (23.9) Loss from discontinued operations before income tax — 1.4 (1.0) (0.6) Gain from disposal of discontinued operations — — — 4.5 Income tax expense / (benefit) from discontinued operations — 0.3 (0.2) 0.8 Net income / (loss) from discontinued operations $ — $ 1.1 $ (0.8) $ 3.1

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Narrative) (Details) $ in Millions	3 Months Ended						9 Months Ended
	Sep. 30, 2021USD ($)	Jun. 30, 2021USD ($)	Mar. 31, 2021USD ($)	Sep. 30, 2020USD ($)	Jun. 30, 2020USD ($)	Mar. 31, 2020USD ($)	Sep. 30, 2021USD ($)mi²customersegment	Sep. 30, 2020USD ($)	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)
Significant Accounting Policies [Line Items]
Number of reportable segments | segment							1
Cash and Cash Equivalents, at Carrying Value	$ 41.5						$ 41.5		$ 25.4
Excise taxes collected	13.5			$ 13.4			37.7	$ 36.7
Restricted Cash and Cash Equivalents, Current	0.1						0.1		0.1
Restricted Cash and Cash Equivalents	41.6			43.6			41.6	43.6	25.5	$ 47
Customer receivables	47.3						47.3		48.5
Unbilled Revenue	15.6						15.6		21.6
Amounts due from partners in jointly owned stations	1.5						1.5		0.2
Due from PJM transmission settlement	1.7						1.7		1.7
Other	3.1						3.1		0.5
Accounts Receivable, Allowance for Credit Loss	(0.9)						(0.9)		(2.8)
Accounts receivable, net	68.3						68.3		69.7
Accounts Receivable, Allowance for Credit Loss, Current	0.9			3.2			0.9	3.2	2.8	0.4
Accounts Receivable, Credit Loss Expense (Reversal)							(0.4)	2.8
Accounts Receivable, Allowance for Credit Loss, Writeoff							(2.6)	(1.4)
Accounts Receivable, Allowance for Credit Loss, Recovery							1.1	1.4
Interest and Debt Expense	(15.8)			(17.1)			(47)	(55.4)
Income Tax Expense (Benefit)	0.8			10.4			0.2	7.7
Net income	8.5		$ 13.6	(8.2)		$ 1.9	22.5	(2.8)
Nonoperating Income (Expense)	(16.6)			(47.8)			(46.7)	(86.2)
Income tax expense / (benefit) from discontinued operations	0			0.3			(0.2)	0.8
Accumulated other comprehensive income	(11.4)						(11.4)		(12.3)
Other Comprehensive Income (Loss), Net of Tax	0.3	$ 0.3	$ 0.3	0.1		(0.3)	0.9	0
Reclassification from AOCI, Current Period, Net of Tax, Attributable to Parent							(0.9)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax	(0.2)			(0.3)			(0.6)	(0.8)
Other Comprehensive Income (Loss), Defined Benefit Plan, Transition Asset (Obligation), Reclassification Adjustment from AOCI, after Tax	0.5			0.3			1.5	0.8
Income tax (expense)/benefit on reclassification of earnings related to derivative activity	0			0			0.1	0.1
Contract with Customer, Asset, before Allowance for Credit Loss	62.9						62.9		70.1
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member]
Significant Accounting Policies [Line Items]
Accumulated other comprehensive income	13						13		13.6
Other Comprehensive Income (Loss), Net of Tax							(0.6)
Change in unfunded pension obligation [Member]
Significant Accounting Policies [Line Items]
Accumulated other comprehensive income	(24.4)						(24.4)		(25.9)
Other Comprehensive Income (Loss), Net of Tax							1.5
Reclassification out of Accumulated Other Comprehensive Income [Member]
Significant Accounting Policies [Line Items]
Net income	0.3			0			0.9	0
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member]
Significant Accounting Policies [Line Items]
Interest and Debt Expense	(0.2)			(0.3)			(0.7)	(0.9)
Income Tax Expense (Benefit)				0				0.1
Net income				(0.3)				(0.8)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Change in unfunded pension obligation [Member]
Significant Accounting Policies [Line Items]
Income Tax Expense (Benefit)				0				(0.1)
Net income				0.3				0.8
Nonoperating Income (Expense)	0.6			0.3			$ 1.9	0.9
Subsidiaries [Member]
Significant Accounting Policies [Line Items]
Number of reportable segments | segment							1
Cash and Cash Equivalents, at Carrying Value	29.8						$ 29.8		11.7
Approximate number of retail customers | customer							533,000
Service area, square miles | mi²							6,000
Number of Operating Segments | segment							1
Excise taxes collected	13.5			13.4			$ 37.7	36.7
Restricted Cash and Cash Equivalents, Current	0.1						0.1		0.1
Restricted Cash and Cash Equivalents	29.9			26.2			29.9	26.2	11.8	21.3
Customer receivables	46.6						46.6		47.6
Unbilled Revenue	15.6						15.6		21.6
Amounts due from partners in jointly owned stations	2.3						2.3		1.9
Due from PJM transmission settlement	1.7						1.7		1.7
Other	3.2						3.2		0.2
Accounts Receivable, Allowance for Credit Loss	(0.9)						(0.9)		(2.8)
Accounts receivable, net	68.5						68.5		70.2
Accounts Receivable, Allowance for Credit Loss, Current	0.9			3.2			0.9	3.2	2.8	$ 0.4
Accounts Receivable, Credit Loss Expense (Reversal)							(0.4)	2.8
Accounts Receivable, Allowance for Credit Loss, Writeoff							2.6	1.4
Interest and Debt Expense	(6.1)			(5.9)			(18.1)	(18.5)
Income Tax Expense (Benefit)	(2.7)			(3.5)			(6.4)	(2.4)
Net income	13.4			17.8			40.3	47.3
Nonoperating Income (Expense)	(7.4)			(5.7)			(19.7)	(19.9)
Accumulated other comprehensive income	(39.2)						(39.2)		(42.1)
Other Comprehensive Income (Loss), Net of Tax	1			0.9	$ 0.9	$ 0.4	2.9	2.2
Reclassification from AOCI, Current Period, Net of Tax, Attributable to Parent							(2.9)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax	0			(0.1)			0	(0.3)
Other Comprehensive Income (Loss), Defined Benefit Plan, Transition Asset (Obligation), Reclassification Adjustment from AOCI, after Tax	1			0.8			2.9	2.4
Income tax (expense)/benefit on reclassification of earnings related to derivative activity	0			(0.1)			0	(0.1)
Income tax (expense)/benefit on reclassification of earnings related to pension and postretirement activity	(0.3)			(0.2)			(0.9)	(0.6)
Contract with Customer, Asset, before Allowance for Credit Loss	62.2						62.2		$ 69.2
Subsidiaries [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Significant Accounting Policies [Line Items]
Net income	1			0.7			2.9	2.1
Subsidiaries [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member]
Significant Accounting Policies [Line Items]
Interest and Debt Expense	0			0			0	(0.2)
Income Tax Expense (Benefit)				(0.1)				(0.1)
Net income	0			(0.1)			0	(0.3)
Subsidiaries [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Change in unfunded pension obligation [Member]
Significant Accounting Policies [Line Items]
Income Tax Expense (Benefit)				(0.2)				(0.6)
Net income	1			0.8			2.9	2.4
Nonoperating Income (Expense)	$ 1.3			$ 1			$ 3.8	$ 3

Regulatory Matters (Details)

Regulatory Matters (Details) - USD ($) $ in Millions	Nov. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Distribution Investment Rider	$ 120.8
Return on Equity SEET Threshold		9.85%
Cash Contribution from Parent Company			$ 150
Transmission System Refund		$ 4.5
Schedule of Regulatory Assets and Liabilities [Text Block]		Regulatory Matters Smart Grid and Comprehensive Settlement On October 23, 2020, AES Ohio entered into a Stipulation and Recommendation (settlement) with the staff of the PUCO and various customers, and organizations representing customers of AES Ohio and certain other parties with respect to, among other matters, AES Ohio's applications pending at the PUCO for (i) approval of AES Ohio's plan to modernize its distribution grid (the Smart Grid Plan), (ii) findings that AES Ohio passed the SEET for 2018 and 2019, and (iii) findings that AES Ohio's current ESP 1 satisfies the SEET and the more favorable in the aggregate (MFA) regulatory test. A hearing was held in January 2021 for consideration of this settlement and on June 16, 2021, the PUCO issued their opinion and order accepting the stipulation as filed. Applications for rehearing of the PUCO's orders relating to the comprehensive settlement were filed on July 16, 2021 and remain pending. Consistent with AES’ earlier statement of intent and based on recent discussions with AES, with the PUCO’s issuance of their opinion and order, DPL and AES Ohio expect that AES will make cash contributions of $150.0 million in 2021 to enable Smart Grid investment. Decoupling On January 23, 2020 AES Ohio filed with the PUCO requesting approval to defer its decoupling costs consistent with the methodology approved in its Distribution Rate Case. If approved, deferral would be effective December 18, 2019 and going forward would reduce impacts of weather, energy efficiency programs and economic changes in customer demand. An evidentiary hearing was held on this matter on May 4, 2021. Distribution Rate Case On November 30, 2020, AES Ohio filed a new Distribution Rate Case with the PUCO. This rate case proposes a revenue increase of $120.8 million per year and incorporates the DIR investments that were planned and approved in the last rate case but not yet included in distribution rates, other distribution investments since September 2015 and investments necessitated by the tornados that occurred on Memorial Day in 2019. The rate case also includes a proposal for increased tree-trimming expenses and certain customer demand-side management programs and recovery of prior-approved regulatory assets for tree trimming, uncollectible expenses and rate case expense. This case is pending a commission order. On July 26, 2021, the PUCO staff filed its Staff Report of Investigation in the distribution rate case. Settlement negotiations are currently ongoing, and the hearing is set to begin on December 7, 2021. FERC Proceedings On March 3, 2020, AES Ohio filed an application before the FERC to change its transmission rate from a stated rate to a formula rate, which was accepted by the FERC and made effective as of May 3, 2020, subject to further proceedings and potential refunds. An uncontested settlement was filed December 10, 2020 and approved April 15, 2021. Among other things, the settlement established new depreciation rates for our transmission assets and an authorized return on equity of 9.85%, and started an amortization process to return excess deferred taxes created by the TCJA. Because the approved settlement rates were lower than the proposed rates that went into effect, AES Ohio has accrued and/or paid refunds of approximately $4.5 million to users of the transmission system in the second quarter and third quarters of 2021 through credits on PJM bills.
Subsidiaries [Member]
Distribution Investment Rider	$ 120.8
Return on Equity SEET Threshold		9.85%
Transmission System Refund		$ 4.5
Schedule of Regulatory Assets and Liabilities [Text Block]		Regulatory Matters Smart Grid and Comprehensive Settlement On October 23, 2020, AES Ohio entered into a Stipulation and Recommendation (settlement) with the staff of the PUCO and various customers, and organizations representing customers of AES Ohio and certain other parties with respect to, among other matters, AES Ohio's applications pending at the PUCO for (i) approval of AES Ohio's plan to modernize its distribution grid (the Smart Grid Plan), (ii) findings that AES Ohio passed the SEET for 2018 and 2019, and (iii) findings that AES Ohio's current ESP 1 satisfies the SEET and the more favorable in the aggregate (MFA) regulatory test. A hearing was held in January 2021 for consideration of this settlement and on June 16, 2021, the PUCO issued their opinion and order accepting the stipulation as filed. Applications for rehearing of the PUCO's orders relating to the comprehensive settlement were filed on July 16, 2021 and remain pending. Consistent with AES’ earlier statement of intent and based on recent discussions with AES, with the PUCO’s issuance of their opinion and order, DPL and AES Ohio expect that AES will make cash contributions of $150.0 million in 2021 to enable Smart Grid investment. Decoupling On January 23, 2020 AES Ohio filed with the PUCO requesting approval to defer its decoupling costs consistent with the methodology approved in its Distribution Rate Case. If approved, deferral would be effective December 18, 2019 and going forward would reduce impacts of weather, energy efficiency programs and economic changes in customer demand. An evidentiary hearing was held on this matter on May 4, 2021. Distribution Rate Case On November 30, 2020, AES Ohio filed a new Distribution Rate Case with the PUCO. This rate case proposes a revenue increase of $120.8 million per year and incorporates the DIR investments that were planned and approved in the last rate case but not yet included in distribution rates, other distribution investments since September 2015 and investments necessitated by the tornados that occurred on Memorial Day in 2019. The rate case also includes a proposal for increased tree-trimming expenses and certain customer demand-side management programs and recovery of prior-approved regulatory assets for tree trimming, uncollectible expenses and rate case expense. This case is pending a commission order. On July 26, 2021, the PUCO staff filed its Staff Report of Investigation in the distribution rate case. Settlement negotiations are currently ongoing, and the hearing is set to begin on December 7, 2021. FERC Proceedings On March 3, 2020, AES Ohio filed an application before the FERC to change its transmission rate from a stated rate to a formula rate, which was accepted by the FERC and made effective as of May 3, 2020, subject to further proceedings and potential refunds. An uncontested settlement was filed December 10, 2020 and approved April 15, 2021. Among other things, the settlement established new depreciation rates for our transmission assets and an authorized return on equity of 9.85%, and started an amortization process to return excess deferred taxes created by the TCJA. Because the approved settlement rates were lower than the proposed rates that went into effect, AES Ohio has accrued and/or paid refunds of approximately $4.5 million to users of the transmission system in the second quarter and third quarters of 2021 through credits on PJM bills.
Forecast [Member]
Cash Contribution from Parent Company		$ 150
Forecast [Member] | Subsidiaries [Member]
Cash Contribution from Parent Company		$ 150

Fair Value (Narrative) (Details

Fair Value (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Unrealized Gain (Loss) on Investments	$ (0.1)	$ 0.3	$ 0.4	$ 0
Subsidiaries [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Unrealized Gain (Loss) on Investments	$ (0.1)	$ 0.3	$ 0.4	$ 0

Fair Value (Fair Value and Cost

Fair Value (Fair Value and Cost of Non-Derivative Instruments) (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Long-term Debt	$ 1,395.1
Subsidiaries [Member]
Long-term Debt	574.2	$ 574.1
Cost [Member]
Total Assets	6.2	6.4
Cost [Member] | Subsidiaries [Member]
Total Assets	6.2	6.4
Fair Value [Member]
Total Assets	9.1	8.9
Investments, Fair Value Disclosure	9.1	8.9
Fair Value [Member] | Subsidiaries [Member]
Total Assets	9.1	8.9
Money Market Funds [Member] | Cost [Member]
6200000	0.4	0.3
Money Market Funds [Member] | Cost [Member] | Subsidiaries [Member]
6200000	0.4	0.3
Money Market Funds [Member] | Fair Value [Member]
Investments, Fair Value Disclosure	0.4	0.3
Money Market Funds [Member] | Fair Value [Member] | Subsidiaries [Member]
Investments, Fair Value Disclosure	0.4	0.3
Equity Securities [Member] | Cost [Member]
6200000	2	2.1
Equity Securities [Member] | Cost [Member] | Subsidiaries [Member]
6200000	2	2.1
Equity Securities [Member] | Fair Value [Member]
Investments, Fair Value Disclosure	4.9	4.5
Equity Securities [Member] | Fair Value [Member] | Subsidiaries [Member]
Investments, Fair Value Disclosure	4.9	4.5
Debt Securities [Member] | Cost [Member]
6200000	3.8	4
Debt Securities [Member] | Cost [Member] | Subsidiaries [Member]
6200000	3.8	4
Debt Securities [Member] | Fair Value [Member]
Investments, Fair Value Disclosure	3.8	4.1
Debt Securities [Member] | Fair Value [Member] | Subsidiaries [Member]
Investments, Fair Value Disclosure	3.8	4.1
Debt [Member] | Cost [Member] | Subsidiaries [Member]
Long-term Debt	574.2	574.1
Debt [Member] | Fair Value [Member]
Debt, Fair Value	1,534	1,571.6
Debt [Member] | Fair Value [Member] | Subsidiaries [Member]
Debt, Fair Value	$ 635.5	$ 656

Fair Value (Fair Value of Asset

Fair Value (Fair Value of Assets and Liabilities Measured on Recurring Basis) (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Level 1 [Member]
Investments, Fair Value Disclosure	$ 0.4	$ 0.3
Total Assets	0.4	0.3
Total Liabilities	0	0
Level 1 [Member] | Subsidiaries [Member]
Total Assets	0.4	0.3
Total Liabilities	0	0
Level 2 [Member]
Investments, Fair Value Disclosure	8.7	8.6
Total Assets	8.7	8.6
Total Liabilities	1,516.8	1,554.2
Level 2 [Member] | Subsidiaries [Member]
Total Assets	8.7	8.6
Total Liabilities	618.3	638.6
Level 3 [Member]
Investments, Fair Value Disclosure	0	0
Total Assets	0	0
Total Liabilities	17.2	17.4
Level 3 [Member] | Subsidiaries [Member]
Total Assets	0	0
Total Liabilities	17.2	17.4
Fair Value [Member]
Investments, Fair Value Disclosure	9.1	8.9
Total Assets	9.1	8.9
Total Liabilities	1,534	1,571.6
Fair Value [Member] | Subsidiaries [Member]
Total Assets	9.1	8.9
Total Liabilities	635.5	656
Money Market Funds [Member] | Level 1 [Member]
Investments, Fair Value Disclosure	0.4	0.3
Money Market Funds [Member] | Level 1 [Member] | Subsidiaries [Member]
Investments, Fair Value Disclosure	0.4	0.3
Money Market Funds [Member] | Level 2 [Member]
Investments, Fair Value Disclosure	0	0
Money Market Funds [Member] | Level 2 [Member] | Subsidiaries [Member]
Investments, Fair Value Disclosure	0	0
Money Market Funds [Member] | Level 3 [Member]
Investments, Fair Value Disclosure	0	0
Money Market Funds [Member] | Level 3 [Member] | Subsidiaries [Member]
Investments, Fair Value Disclosure	0	0
Money Market Funds [Member] | Fair Value [Member]
Investments, Fair Value Disclosure	0.4	0.3
Money Market Funds [Member] | Fair Value [Member] | Subsidiaries [Member]
Investments, Fair Value Disclosure	0.4	0.3
Equity Securities [Member] | Level 1 [Member]
Investments, Fair Value Disclosure	0	0
Equity Securities [Member] | Level 1 [Member] | Subsidiaries [Member]
Investments, Fair Value Disclosure	0	0
Equity Securities [Member] | Level 2 [Member]
Investments, Fair Value Disclosure	4.9	4.5
Equity Securities [Member] | Level 2 [Member] | Subsidiaries [Member]
Investments, Fair Value Disclosure	4.9	4.5
Equity Securities [Member] | Level 3 [Member]
Investments, Fair Value Disclosure	0	0
Equity Securities [Member] | Level 3 [Member] | Subsidiaries [Member]
Investments, Fair Value Disclosure	0	0
Equity Securities [Member] | Fair Value [Member]
Investments, Fair Value Disclosure	4.9	4.5
Equity Securities [Member] | Fair Value [Member] | Subsidiaries [Member]
Investments, Fair Value Disclosure	4.9	4.5
Debt Securities [Member] | Level 1 [Member]
Investments, Fair Value Disclosure	0	0
Debt Securities [Member] | Level 1 [Member] | Subsidiaries [Member]
Investments, Fair Value Disclosure	0	0
Debt Securities [Member] | Level 2 [Member]
Investments, Fair Value Disclosure	3.8	4.1
Debt Securities [Member] | Level 2 [Member] | Subsidiaries [Member]
Investments, Fair Value Disclosure	3.8	4.1
Debt Securities [Member] | Level 3 [Member]
Investments, Fair Value Disclosure	0	0
Debt Securities [Member] | Level 3 [Member] | Subsidiaries [Member]
Investments, Fair Value Disclosure	0	0
Debt Securities [Member] | Fair Value [Member]
Investments, Fair Value Disclosure	3.8	4.1
Debt Securities [Member] | Fair Value [Member] | Subsidiaries [Member]
Investments, Fair Value Disclosure	3.8	4.1
Debt [Member] | Level 1 [Member]
Debt	0	0
Debt [Member] | Level 1 [Member] | Subsidiaries [Member]
Debt	0	0
Debt [Member] | Level 2 [Member]
Debt	1,516.8	1,554.2
Debt [Member] | Level 2 [Member] | Subsidiaries [Member]
Debt	618.3	638.6
Debt [Member] | Level 3 [Member]
Debt	17.2	17.4
Debt [Member] | Level 3 [Member] | Subsidiaries [Member]
Debt	17.2	17.4
Debt [Member] | Fair Value [Member]
Debt	1,534	1,571.6
Debt [Member] | Fair Value [Member] | Subsidiaries [Member]
Debt	$ 635.5	$ 656

Derivative Instruments and He_3

Derivative Instruments and Hedging Activities (Narrative) (Details) $ in Millions	Aug. 03, 2020USD ($)Number_of_interest_rate_swaps
Subsidiaries [Member]
Debt Instrument, Number of Financial Covenants | Number_of_interest_rate_swaps	2
One Point One Three To One Point One Seven Bonds Maturing In August Two Thousand Twenty [Member]
Long-term Debt, Gross	$ 140
One Point One Three To One Point One Seven Bonds Maturing In August Two Thousand Twenty [Member] | Subsidiaries [Member]
Long-term Debt, Gross	140
Interest Rate Swap [Member] | Designated as Hedging Instrument [Member]
Derivative, Notional Amount, Purchase (Sales), Net	140
Interest Rate Swap [Member] | Designated as Hedging Instrument [Member] | Subsidiaries [Member]
Derivative, Notional Amount, Purchase (Sales), Net	$ 140

Derivative Instruments and He_4

Derivative Instruments and Hedging Activities (Outstanding Derivative Instruments) (Details) - Designated as Hedging Instrument [Member] - Interest Rate Swap [Member] $ in Millions	Aug. 03, 2020USD ($)
Derivative, Notional Amount, Purchase (Sales), Net	$ 140
Subsidiaries [Member]
Derivative, Notional Amount, Purchase (Sales), Net	$ 140

Derivative Instruments and He_5

Derivative Instruments and Hedging Activities (Gains or Losses Recognized in AOCI for the Cash Flow Hedges) (Details) - Interest Rate Contract [Member] - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Accumulated Derivative Gain/Loss in AOCI [Roll Forward]
Beginning accumulated derivative gain / (loss) in AOCI	$ 13.2	$ 13.9	$ 13.6	$ 14.5
Net gains / (losses) associated with current period hedging transactions	0	0.1	0	0
Ending accumulated derivative gain / (loss) in AOCI	13	13.7	13	13.7
Portion expected to be reclassified to earnings in the next twelve months	$ (0.8)		$ (0.8)
Subsidiaries [Member]
Accumulated Derivative Gain/Loss in AOCI [Roll Forward]
Beginning accumulated derivative gain / (loss) in AOCI		(0.7)		(0.4)
Net gains / (losses) associated with current period hedging transactions		0.2		0.1
Ending accumulated derivative gain / (loss) in AOCI		(0.6)		(0.6)
Interest Expense [Member]
Accumulated Derivative Gain/Loss in AOCI [Roll Forward]
Net gains losses reclassified to earnings		(0.3)		(0.8)
Interest Expense [Member] | Subsidiaries [Member]
Accumulated Derivative Gain/Loss in AOCI [Roll Forward]
Net gains losses reclassified to earnings		$ (0.1)		$ (0.3)

Derivative Instruments and He_6

Derivative Instruments and Hedging Activities (Fair Value and Balance Sheet Location (Details) - Designated as Hedging Instrument [Member] - Interest Rate Swap [Member] $ in Millions	Aug. 03, 2020USD ($)
Derivative, Notional Amount, Purchase (Sales), Net	$ 140
Subsidiaries [Member]
Derivative, Notional Amount, Purchase (Sales), Net	$ 140

Debt (Narrative) (Details)

Debt (Narrative) (Details) $ in Millions	9 Months Ended
	Sep. 30, 2021USD ($)debt_covenantfiscal_quarter	Sep. 30, 2020USD ($)	Dec. 31, 2022USD ($)	Sep. 30, 2022USD ($)	Dec. 31, 2020USD ($)	Aug. 03, 2020USD ($)	Jun. 01, 2020USD ($)
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity		$ 110
Long-term Line of Credit	$ 80				$ 80
Debt Covenant, Leverage Ratio, Maximum	0.67
Debt Covenant, Interest Coverage Ratio, Minimum	1.70						2.25
Proceeds from Issuance of Long-term Debt	$ 0	555
Debt Instrument, Debt Covenant, EBITDA to Interest Expense, EBITDA Minimum	$ 125	125
Debt Instrument, Debt Covenant, Total Debt to EBITDA Ratio	7
Line of Credit Facility, quarterly borrowing limit reduction	$ 5
Line of Credit Facility, Current Borrowing Capacity							$ 125
Less: current portion	(0.2)				(0.2)
Debt Instrument, Unamortized Discount (Premium), Net	(0.9)				(0.9)
Debt Instrument, Debt Covenant, Total Debt to EBITDA, Borrowing Limit	110
Debt Instrument, Debt Covenant, Total Debt to EBITDA, New Borrowing Limit	105
Debt Instrument, Debt Covenant, Total Debt to EBITDA, Borrowing Limit Quarterly Reduction	5
Phase 1 [Member]
Debt Instrument [Line Items]
Debt Instrument, Debt Covenant, EBITDA to Interest Expense, EBITDA Minimum				$ 130
Phase 2 [Member]
Debt Instrument [Line Items]
Debt Instrument, Debt Covenant, EBITDA to Interest Expense, EBITDA Minimum			$ 150
Forecast [Member]
Debt Instrument [Line Items]
Debt Covenant, Interest Coverage Ratio, Minimum			2	1.75
Debt Instrument, Debt Covenant, EBITDA to Interest Expense, EBITDA Minimum			$ 150	$ 130
Subsidiaries [Member]
Debt Instrument [Line Items]
Long-term Line of Credit	140				20
Proceeds from Issuance of Long-term Debt	0	$ 140
Less: current portion	(0.2)				(0.2)
Deferred Finance Costs, Net, Including Acquisition Adjustments	(5.5)				(5.7)
Debt Instrument, Unamortized Discount (Premium), Net	(2.5)				(2.6)
3.95% Senior Notes due 2049 [Member] | Subsidiaries [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 425				425
Debt Instrument, Interest Rate, Effective Percentage	3.95%
Variable Rate Notes Backed by Term Loan and First Mortgage Bonds [Member] | Subsidiaries [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 140					$ 140
DPL Revolving Credit Agreement and Term Loan Maturing July 2020 [Member]
Debt Instrument [Line Items]
Number of financial covenants | debt_covenant	2
Number of prior quarters included in EBITDA to interest calculation | fiscal_quarter	4
Debt Covenant, Interest Coverage Ratio, Minimum	2.50
Ten Year Senior Unsecured Notes At725 Maturing At October152021 [Member]
Debt Instrument [Line Items]
Debt instrument interest percentage		7.25%
Make Whole Premium		$ 30.8
Extinguishment of Debt, Amount		$ 380
Revolving Credit Facility [Member] | Subsidiaries [Member]
Debt Instrument [Line Items]
Debt Covenant, Debt to EBITDA Ratio, Maximum	7
Debt Covenant, Total Debt to Total Capitalization Ratio, Maximum	0.67
4.125% Senior Notes due 2025 [Member]
Debt Instrument [Line Items]
Debt instrument interest percentage		4.125%
Proceeds from Issuance of Long-term Debt		$ 415
3.25% First Mortgage Bonds due 2040 [Member] | Subsidiaries [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 140				$ 140
Debt instrument interest percentage	3.20%
Proceeds from Issuance of Long-term Debt		$ 140
Debt Instrument, Interest Rate, Effective Percentage	3.20%
One Point One Three To One Point One Seven Bonds Maturing In August Two Thousand Twenty [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross						140
One Point One Three To One Point One Seven Bonds Maturing In August Two Thousand Twenty [Member] | Subsidiaries [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross						$ 140

Debt (Long-term Debt) (Details)

Debt (Long-term Debt) (Details) $ in Millions	9 Months Ended
	Sep. 30, 2021USD ($)	Sep. 30, 2020USD ($)	Dec. 31, 2022USD ($)	Sep. 30, 2022USD ($)	Dec. 31, 2020USD ($)	Aug. 03, 2020USD ($)	Jun. 01, 2020
Debt Instrument [Line Items]
Unamortized deferred finance costs	$ (8.8)				$ (10.2)
Unamortized debt discounts, net	(0.9)				(0.9)
Total long-term debt	1,395.1
Less: current portion	(0.2)				(0.2)
Long-term debt	1,394.9				1,393.4
Long-term Line of Credit	$ 80				80
Debt Covenant, Interest Coverage Ratio, Minimum	1.70						2.25
Debt Instrument, Debt Covenant, EBITDA to Interest Expense, EBITDA Minimum	$ 125	$ 125
Proceeds from Issuance of Long-term Debt	$ 0	555
Long-term Debt	Long-term Debt Long-term debt is as follows: Interest September 30, December 31, $ in millions Rate Maturity 2021 2020 First Mortgage Bonds 3.95% 2049 $ 425.0 $ 425.0 First Mortgage Bonds 3.20% 2040 140.0 140.0 U.S. Government note 4.20% 2061 17.2 17.4 Unamortized deferred financing costs (5.5) (5.7) Unamortized debt discounts, net (2.5) (2.6) Total long-term debt at AES Ohio 574.2 574.1 Senior unsecured bonds 4.125% 2025 415.0 415.0 Senior unsecured bonds 4.35% 2029 400.0 400.0 Note to DPL Capital Trust II (a) 8.125% 2031 15.6 15.6 Unamortized deferred financing costs (8.8) (10.2) Unamortized debt discounts, net (0.9) (0.9) Total long-term debt 1,395.1 1,393.6 Less: current portion (0.2) (0.2) Long-term debt, net of current portion $ 1,394.9 $ 1,393.4 (a) Note payable to related party. Lines of credit As of September 30, 2021 and December 31, 2020, the DPL Credit Agreement had outstanding borrowings of $80.0 million and $80.0 million, respectively. As of September 30, 2021 and December 31, 2020, the AES Ohio Credit Agreement had outstanding borrowings of $140.0 million and $20.0 million, respectively. Significant transactions On July 31, 2020, AES Ohio issued $140.0 million of taxable First Mortgage Bonds and on August 3, 2020 used the proceeds to purchase at par value the $140.0 million of outstanding tax-exempt Ohio Air Quality Development Authority (OAQDA) Collateralized Pollution Control Revenue Refunding Bonds that had been issued in 2015. The new taxable First Mortgage Bonds carry an interest rate of 3.20% and mature on July 31, 2040. The OAQDA Revenue bonds have not been legally cancelled and can be re-issued at the discretion of AES Ohio at any time. These bonds will be held in trust while we continue to evaluate market conditions and explore suitable long-term financing alternatives. Accordingly, as of September 30, 2021 and December 31, 2020, the $140.0 million variable rate OAQDA Revenue bonds are not treated as being outstanding in the Condensed Consolidated Balance Sheet. On June 19, 2020, DPL closed a $415.0 million issuance of senior unsecured notes. These notes carry an interest rate of 4.125% and mature on July 1, 2025. Proceeds from the issuance and cash on hand were used to redeem in-full the remaining balance of $380.0 million of DPL's 7.25% senior unsecured notes. These bonds were redeemed at par plus accrued interest and a make-whole premium of $30.8 million on July 20, 2020. DPL agreed to register the 2025 DPL Senior Unsecured Bonds under the Securities Act by filing an exchange offer registration statement or, under specified circumstances, a shelf registration statement with the SEC pursuant to a Registration Rights Agreement dated June 19, 2020. DPL filed a registration statement on Form S-4 with respect to the 2025 DPL Senior Unsecured Bonds with the SEC on March 15, 2021, and this registration statement was declared effective on March 31, 2021. The exchange offer closed on May 5, 2021. On June 1, 2020, the DPL Credit Agreement was amended. As a result of the amendment, the borrowing limit was reduced from $125.0 million to $110.0 million, the Total Debt to EBITDA covenant was eliminated, the EBITDA to Interest Expense covenant was reduced from 2.25 to 1.00 to 1.70 to 1.00, increasing to 1.75 to 1.00 as of September 30, 2022 and 2.00 to 1.00 as of December 31, 2022, and a trailing-twelve months minimum EBITDA covenant of $125.0 million was added, increasing to $130.0 million as of September 30, 2022 and $150.0 million as of December 31, 2022. Starting with the quarter ended September 30, 2021, the borrowing limit will be reduced by $5.0 million per quarter should DPL’s Total Debt to EBITDA ratio calculated for the period of four consecutive quarters exceed 7.00 to 1.00. Long-term debt covenants and restrictions The DPL Credit Agreement has two financial covenants. The first financial covenant, a minimum EBITDA, calculated at the end of each fiscal quarter for the four prior fiscal quarters, of $125.0 million is required, stepping up to $130.0 million on September 30, 2022 and $150.0 million on December 31, 2022. As of September 30, 2021, DPL was in compliance with this financial covenant. The second financial covenant is an EBITDA to Interest Expense ratio that is calculated, at the end of each fiscal quarter, by dividing EBITDA for the four prior fiscal quarters by the consolidated interest charges for the same period. The ratio, per the agreement, is to be not less than 1.70 to 1.00, and steps up to 1.75 to 1.00 on September 30, 2022 and 2.00 to 1.00 as of December 31, 2022. As of September 30, 2021, DPL was in compliance with this financial covenant. The DPL Credit Agreement also restricts dividend payments from DPL to AES, such that DPL cannot make dividend payments unless at the time of, and/or as a result of the distribution, (i) DPL’s leverage ratio does not exceed 0.67 to 1.00 and DPL’s interest coverage ratio is not less than 2.50 to 1.00 or, if such ratios are not within the parameters, (ii) DPL’s senior long-term debt rating from two of the three major credit rating agencies is at least investment grade. As a result, as of September 30, 2021, DPL was prohibited from making a distribution to its shareholder or making a loan to any of its affiliates (other than its subsidiaries). Starting with the quarter ended September 30, 2021, the borrowing limit on the DPL Credit Agreement will be reduced by $5.0 million per quarter should the Total Debt to EBITDA ratio for the period of four consecutive quarters exceed 7.00 to 1.00. As of September 30, 2021, DPL exceeded this ratio and the borrowing limit was reduced from $110.0 million to $105.0 million. The AES Ohio Credit Agreement and Bond Purchase Agreement (financing document entered into in connection with the issuance of AES Ohio's First Mortgage Bonds, on July 31, 2020) has one financial covenant. The covenant measures Total Debt to Total Capitalization and is calculated, at the end of each fiscal quarter, by dividing total debt at the end of the quarter by total capitalization at the end of the quarter. AES Ohio’s Total Debt to Total Capitalization ratio shall not be greater than 0.67 to 1.00. As of September 30, 2021, AES Ohio was in compliance with this financial covenant. As of September 30, 2021, DPL and AES Ohio were in compliance with all debt covenants, including the financial covenants described above. AES Ohio does not have any meaningful restrictions in its debt financing documents prohibiting dividends and return of capital payments to its parent, DPL. Substantially all property, plant & equipment of AES Ohio is subject to the lien of the mortgage securing AES Ohio’s First and Refunding Mortgage.
Forecast [Member]
Debt Instrument [Line Items]
Debt Covenant, Interest Coverage Ratio, Minimum			2	1.75
Debt Instrument, Debt Covenant, EBITDA to Interest Expense, EBITDA Minimum			$ 150	$ 130
Subsidiaries [Member]
Debt Instrument [Line Items]
Unamortized deferred finance costs	$ (5.5)				(5.7)
Unamortized debt discounts, net	(2.5)				(2.6)
Total long-term debt at subsidiary	574.2				574.1
Total long-term debt	574.2				574.1
Less: current portion	(0.2)				(0.2)
Long-term debt	574				573.9
Long-term Line of Credit	140				20
Proceeds from Issuance of Long-term Debt	$ 0	$ 140
Long-term Debt	Long-term Debt Long-term debt is as follows: Interest September 30, December 31, $ in millions Rate Maturity 2021 2020 First Mortgage Bonds 3.95 % 2049 $ 425.0 $ 425.0 First Mortgage Bonds 3.20 % 2040 140.0 140.0 U.S. Government note 4.20 % 2061 17.2 17.4 Unamortized deferred financing costs (5.5) (5.7) Unamortized debt discounts, net (2.5) (2.6) Total long-term debt 574.2 574.1 Less: current portion (0.2) (0.2) Long-term debt, net of current portion $ 574.0 $ 573.9 Line of credit As of September 30, 2021 and December 31, 2020, the AES Ohio Credit Agreement had outstanding borrowings on its line of credit of $140.0 million and $20.0 million, respectively. Significant transactions On July 31, 2020, AES Ohio issued $140.0 million of taxable First Mortgage Bonds and on August 3, 2020 used the proceeds to purchase at par value the $140.0 million of outstanding tax-exempt Ohio Air Quality Development Authority (OAQDA) Collateralized Pollution Control Revenue Refunding Bonds that had been issued in 2015. The new taxable First Mortgage Bonds carry an interest rate of 3.20% and mature on July 31, 2040. The OAQDA Revenue bonds have not been legally cancelled and can be re-issued at the discretion of AES Ohio at any time. These bonds will be held in trust while we continue to evaluate market conditions and explore suitable long-term financing alternatives. Accordingly, as of September 30, 2021 and December 31, 2020, the $140.0 million variable rate OAQDA Revenue bonds are not treated as being outstanding in the Condensed Consolidated Balance Sheet. Long-term debt covenants and restrictions The AES Ohio Credit Agreement and Bond Purchase Agreement (financing document entered into in connection with the issuance of AES Ohio's First Mortgage Bonds, on July 31, 2020) has one financial covenant. The covenant measures Total Debt to Total Capitalization and is calculated, at the end of each fiscal quarter, by dividing total debt at the end of the quarter by total capitalization at the end of the quarter. AES Ohio’s Total Debt to Total Capitalization ratio shall not be greater than 0.67 to 1.00. As of September 30, 2021, AES Ohio was in compliance with this financial covenant. As of September 30, 2021, AES Ohio was in compliance with all debt covenants, including the financial covenants described above. AES Ohio does not have any meaningful restrictions in its debt financing documents prohibiting dividends and return of capital payments to its parent, DPL. Substantially all property, plant & equipment of AES Ohio is subject to the lien of the mortgage securing AES Ohio’s First and Refunding Mortgage.
3.95% Senior Notes due 2049 [Member] | Subsidiaries [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage	3.95%
Long-term Debt, Gross	$ 425				425
DPL Revolving Credit Agreement and Term Loan Maturing July 2020 [Member]
Debt Instrument [Line Items]
Debt Covenant, Interest Coverage Ratio, Minimum	2.50
Pollution Control Series Maturing in August 2020 - 1.13% - 1.14% [Member] | Subsidiaries [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 140					$ 140
U.S. Government note maturing in February 2061 - 4.20% [Member] | Subsidiaries [Member]
Debt Instrument [Line Items]
Debt instrument interest percentage	4.20%
Long-term Debt, Gross	$ 17.2				17.4
Senior unsecured due in October 2021 - 7.25% [Member]
Debt Instrument [Line Items]
Debt instrument interest percentage		7.25%
4.35% Senior Notes due 2029 [Member]
Debt Instrument [Line Items]
Debt instrument interest percentage	4.35%
Long-term Debt, Gross	$ 400				400
Note to DPL Capital Trust II Maturing in September 2031 - 8.125% [Member]
Debt Instrument [Line Items]
Debt instrument interest percentage	8.125%
Long-term Debt, Gross	$ 15.6				15.6
4.13% Senior Notes due 2025
Debt Instrument [Line Items]
Debt instrument interest percentage	4.125%
Long-term Debt, Gross	$ 415				415
4.125% Senior Notes due 2025 [Member]
Debt Instrument [Line Items]
Debt instrument interest percentage		4.125%
Proceeds from Issuance of Long-term Debt		$ 415
3.25% First Mortgage Bonds due 2040 [Member] | Subsidiaries [Member]
Debt Instrument [Line Items]
Debt instrument interest percentage	3.20%
Debt Instrument, Interest Rate, Effective Percentage	3.20%
Proceeds from Issuance of Long-term Debt		$ 140
Long-term Debt, Gross	$ 140				$ 140
One Point One Three To One Point One Seven Bonds Maturing In August Two Thousand Twenty [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross						140
One Point One Three To One Point One Seven Bonds Maturing In August Two Thousand Twenty [Member] | Subsidiaries [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross						$ 140

Income Taxes (Narrative) (Detai

Income Taxes (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Entity Information [Line Items]
Effective Income Tax Rate Reconciliation, at Combined Federal and State Statutory Income Tax Rate, Percent			22.50%
Effective Income Tax Rate Reconciliation, Including Discontinued Operations, Percent	(10.40%)	55.20%	(1.80%)	71.10%
Unrecognized Tax Benefits	$ 1.4		$ 1.4
Unrecognized Tax Benefits Due to Uncertainty In Timing of Deductibility	1.4		1.4
Unrecognized tax benefits anticipated to result in a decrease in effective tax rate in the period the position is released	$ 0.5		$ 0.5
Subsidiaries [Member]
Entity Information [Line Items]
Effective income tax rates		16.40%		4.80%
Effective Income Tax Rate Reconciliation, at Combined Federal and State Statutory Income Tax Rate, Percent			22.50%
Effective Income Tax Rate Reconciliation, Including Discontinued Operations, Percent	16.80%		13.70%
Unrecognized Tax Benefits	$ 1.4		$ 1.4
Unrecognized Tax Benefits Due to Uncertainty In Timing of Deductibility	1.4		1.4
Unrecognized tax benefits anticipated to result in a decrease in effective tax rate in the period the position is released	$ 0.5		$ 0.5

Benefit Plans (Net Periodic Ben

Benefit Plans (Net Periodic Benefit Cost (Income)) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Pension [Member]
Contributions by employer			$ 9.8	$ 7.5
Service cost	$ 1.2	$ 0.9	3.4	2.8
Interest cost	2.1	2.9	6.1	8.8
Expected return on assets	(3.8)	(4.6)	(11.2)	(14)
Prior service cost	0.2	0.3	0.6	0.8
Actuarial loss / (gain)	2.2	1.5	6.8	4.6
Net periodic benefit cost	1.9	1	5.7	3
Postretirement [Member]
Defined Benefit Plan, Funded (Unfunded) Status of Plan	8.3		8.3		$ 9
Subsidiaries [Member] | Pension [Member]
Contributions by employer			9.8	7.5
Service cost	1.2	0.9	3.4	2.8
Interest cost	2.1	2.9	6.1	8.8
Expected return on assets	(3.8)	(4.6)	(11.2)	(14)
Prior service cost	0.2	0.3	0.8	1
Actuarial loss / (gain)	2.9	2.2	8.5	6.5
Net periodic benefit cost	2.6	$ 1.7	7.6	$ 5.1
Subsidiaries [Member] | Postretirement [Member]
Defined Benefit Plan, Funded (Unfunded) Status of Plan	$ 8.3		$ 8.3		$ 9

Benefit Plans (Estimated Future

Benefit Plans (Estimated Future Benefit Payments and Medicare Part D Reimbursements) (Details) - Postretirement [Member] - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Defined Benefit Plan, Funded (Unfunded) Status of Plan	$ 8.3	$ 9
Subsidiaries [Member]
Defined Benefit Plan, Funded (Unfunded) Status of Plan	$ 8.3	$ 9

Shareholder's Equity (Details)

Shareholder's Equity (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended				9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Sep. 30, 2020	Jun. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Class of Stock [Line Items]
Stockholders' Equity Note Disclosure					Shareholder's Deficit Capital Contributions from AES There were no capital contributions during the nine months ended September 30, 2021. During the nine months ended September 30, 2020, DPL received $150.0 million in a cash contribution from AES, which DPL then used to make a $150.0 million capital contribution to AES Ohio . The contribution at DPL represented an equity capital contribution of $98.0 million and a payment of $52.0 million against its tax receivable. The proceeds from the capital contribution at AES Ohio will primarily be used for funding needs to support AES Ohio's capital expenditure program, mainly new investments in and upgrades to AES Ohio’s transmission and distribution system.
Non-cash capital contribution				$ 98
Common Stock, Shares Authorized	1,500				1,500		1,500
Proceeds from Contributions from Parent					$ 0	$ 98
Cash Contribution from Parent Company						150
Payment against tax receivable balance from Parent						52
Proceeds from Contributions from Parent					$ 0	98
Other Additional Capital [Member]
Class of Stock [Line Items]
Non-cash capital contribution				98
Subsidiaries [Member]
Class of Stock [Line Items]
Stockholders' Equity Note Disclosure					Shareholder's Equity Capital Contribution and Returns of Capital During the nine months ended September 30, 2021, AES Ohio made return of capital payments of $27.0 million to DPL , of which $17.0 million was declared in 2021. DPL made a capital contribution of $150.0 million to AES Ohio. The proceeds are primarily being used to support AES Ohio's capital expenditure program, consisting primarily of investments in and upgrades to AES Ohio’s transmission and distribution system. Additionally, AES Ohio declared return of capital payments of up to $42.7 million to DPL , of which $27.7 million was paid during the period.
Common Stock, Shares Authorized	50,000,000				50,000,000		50,000,000
Par value common shares (in USD per share)	$ 0.01				$ 0.01		$ 0.01
Common Stock, Shares, Outstanding	41,172,173				41,172,173		41,172,173
Proceeds from Contributions from Parent				150	$ 0	150
Dividends, Common Stock, Cash	$ (10)	$ (7)	$ (28.5)	(14.2)		(42.7)
Dividends, Common Stock, Cash	10	7	28.5	14.2		42.7
Payments of Ordinary Dividends, Common Stock					27	27.7
Proceeds from Contributions from Parent				150	0	$ 150
Subsidiaries [Member] | Other Additional Capital [Member]
Class of Stock [Line Items]
Proceeds from Contributions from Parent				150
Dividends, Common Stock, Cash	(10)	(7)	(28.5)	(14.2)	(17)
Dividends, Common Stock, Cash	$ 10	$ 7	$ 28.5	14.2	$ 17
Proceeds from Contributions from Parent				$ 150

Contractual Obligations, Comm_2

Contractual Obligations, Commercial Commitments and Contingencies (Narrative) (Details) - Subsidiaries [Member] $ in Millions	Sep. 30, 2021USD ($)
Debt Obligation on 4.9% Equity Ownership [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Equity ownership interest	4.90%
Equity ownership interest aggregate cost	$ 55.9
Electric Generation Company [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Debt obligation	$ 1,140.5

Business Segments (Narrative) (

Business Segments (Narrative) (Details) $ in Millions	9 Months Ended
	Sep. 30, 2021USD ($)mi²customersegment	Dec. 31, 2020USD ($)
Segment Reporting Information [Line Items]
Total assets	$ 2,088.7	$ 2,036
Subsidiaries [Member]
Segment Reporting Information [Line Items]
Number of Operating Segments | segment	1
Approximate number of retail customers | customer	533,000
Service area, square miles | mi²	6,000
Total assets	$ 2,067.6	2,014.7
Operating Segments [Member] | Utility [Member]
Segment Reporting Information [Line Items]
Total assets		2,014.7
Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Total assets	$ 21.1	$ 21.3

Business Segments (Segment Fina

Business Segments (Segment Financial Information) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Segment Reporting Information [Line Items]
External customer revenues	$ 188.2	$ 178.8	$ 511.5	$ 505.1
Intersegment revenues	0	0	0	0
Total revenues	188.2	178.8	511.5	505.1
Depreciation and amortization	18.9	18.6	56.9	54.8
Interest expense	15.8	17.1	47	55.4
Gain (Loss) on Extinguishment of Debt	0	31.7	0	31.7
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	7.7	(19.7)	23.1	(13.6)
Total assets	2,088.7		2,088.7		$ 2,036
Operating Segments [Member] | Utility [Member]
Segment Reporting Information [Line Items]
External customer revenues	185.9	176.8	504.2	498.4
Intersegment revenues	0.2	0.2	0.6	0.7
Total revenues	186.1	177	504.8	499.1
Depreciation and amortization	18.6	18.2	55.8	53.7
Interest expense	6.1	5.9	18.1	18.5
Gain (Loss) on Extinguishment of Debt		0		0
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	16.1	21.3	46.7	49.7
Total assets					2,014.7
Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
External customer revenues	2.3	2	7.3	6.7
Intersegment revenues	0.8	1	2.6	2.7
Total revenues	3.1	3	9.9	9.4
Depreciation and amortization	0.3	0.4	1.1	1.1
Interest expense	9.7	11.2	28.9	36.9
Gain (Loss) on Extinguishment of Debt		31.7		31.7
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	(8.4)	(41)	(23.6)	(63.3)
Total assets	21.1		21.1		21.3
Adjustments and Eliminations [Member]
Segment Reporting Information [Line Items]
External customer revenues	0	0		0
Intersegment revenues	(1)	(1.2)	(3.2)	(3.4)
Total revenues	(1)	(1.2)	(3.2)	(3.4)
Depreciation and amortization	0	0	0	0
Interest expense	0	0	0	0
Gain (Loss) on Extinguishment of Debt		0		0
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	0	0	0	0
Subsidiaries [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization	18.6	18.2	55.8	53.7
Interest expense	6.1	5.9	18.1	18.5
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	16.1	$ 21.3	46.7	$ 49.7
Total assets	$ 2,067.6		$ 2,067.6		$ 2,014.7

Revenue (Details)

Revenue (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Revenue from Contract with Customer, Excluding Assessed Tax	$ 187.5	$ 177	$ 507	$ 492.3
RTO Revenue	12.5	11.4	39.5	32.3
RTO Capacity Revenue	1.8	0.9	4	3.2
Revenues	188.2	178.8	511.5	505.1
Contract with Customer, Asset, before Allowance for Credit Loss	62.9		62.9		$ 70.1
Subsidiaries [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	185.3	175.2	500.3	486.3
RTO Revenue	12.5	11.5	39.4	32.3
RTO Capacity Revenue	1.8	0.9	4	3.2
Revenues	186.1	177	504.8	499.1
Contract with Customer, Asset, before Allowance for Credit Loss	62.2		62.2		$ 69.2
Utility [Member]
RTO Revenue	12.5	11.5	39.4	32.3
RTO Capacity Revenue	1.8	0.9	4	3.2
Revenues	186.1	177	504.8	499.1
Corporate and Other
RTO Revenue	0	(0.1)	0.1	0
RTO Capacity Revenue	0	0	0	0
Revenues	3.1	3	9.9	9.4
Adjustments and Eliminations
RTO Revenue	0	0	0	0
RTO Capacity Revenue	0	0	0	0
Revenues	(1)	(1.2)	(3.2)	(3.4)
Other Revenues [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	2.4	2.1	7.2	6.7
Other non-606 revenue	0.7	1.7	4.5	4
Other Revenues [Member] | Subsidiaries [Member]
Other non-606 revenue	0.8	1.7	4.5	4
Other Revenues [Member] | Utility [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	0	0	0	0
Other non-606 revenue	0.8	1.7	4.5	4
Other Revenues [Member] | Corporate and Other
Revenue from Contract with Customer, Excluding Assessed Tax	2.4	2.1	7.2	6.7
Other non-606 revenue	0.7	1	2.6	2.7
Other Revenues [Member] | Adjustments and Eliminations
Revenue from Contract with Customer, Excluding Assessed Tax	0	0	0	0
Other non-606 revenue	(0.8)	(1)	(2.6)	(2.7)
Wholesale Revenue [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	6.6	3	14.8	7
Wholesale Revenue [Member] | Subsidiaries [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	6.8	3.2	15.4	7.7
Wholesale Revenue [Member] | Utility [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	6.8	3.2	15.4	7.7
Wholesale Revenue [Member] | Corporate and Other
Revenue from Contract with Customer, Excluding Assessed Tax	0	0	0	0
Wholesale Revenue [Member] | Adjustments and Eliminations
Revenue from Contract with Customer, Excluding Assessed Tax	(0.2)	(0.2)	(0.6)	(0.7)
Retail Revenue [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	164.2	159.6	441.5	443.1
Other non-606 revenue		0.1		8.8
Retail Revenue [Member] | Residential Revenue
Revenue from Contract with Customer, Excluding Assessed Tax	103.3	99.3	279.3	279.9
Retail Revenue [Member] | Commercial Revenue
Revenue from Contract with Customer, Excluding Assessed Tax	35	32.2	90.5	87.6
Retail Revenue [Member] | Industrial Revenue
Revenue from Contract with Customer, Excluding Assessed Tax	16	14.5	42.4	38.2
Retail Revenue [Member] | Governmental Revenue
Revenue from Contract with Customer, Excluding Assessed Tax	7	9.9	19.9	27.7
Retail Revenue [Member] | Other Revenues [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	2.9	3.7	9.4	9.7
Retail Revenue [Member] | Utility [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	164.2	159.6	441.5	443.1
Other non-606 revenue	0	0.1	0	8.8
Retail Revenue [Member] | Utility [Member] | Residential Revenue
Revenue from Contract with Customer, Excluding Assessed Tax	103.3	99.3	279.3	279.9
Retail Revenue [Member] | Utility [Member] | Commercial Revenue
Revenue from Contract with Customer, Excluding Assessed Tax	35	32.2	90.5	87.6
Retail Revenue [Member] | Utility [Member] | Industrial Revenue
Revenue from Contract with Customer, Excluding Assessed Tax	16	14.5	42.4	38.2
Retail Revenue [Member] | Utility [Member] | Governmental Revenue
Revenue from Contract with Customer, Excluding Assessed Tax	7	9.9	19.9	27.7
Retail Revenue [Member] | Utility [Member] | Other Revenues [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	2.9	3.7	9.4	9.7
Retail Revenue [Member] | Corporate and Other
Revenue from Contract with Customer, Excluding Assessed Tax	0	0	0	0
Other non-606 revenue		0		0
Retail Revenue [Member] | Corporate and Other | Residential Revenue
Revenue from Contract with Customer, Excluding Assessed Tax	0	0	0	0
Retail Revenue [Member] | Corporate and Other | Commercial Revenue
Revenue from Contract with Customer, Excluding Assessed Tax	0	0	0	0
Retail Revenue [Member] | Corporate and Other | Industrial Revenue
Revenue from Contract with Customer, Excluding Assessed Tax	0	0	0	0
Retail Revenue [Member] | Corporate and Other | Governmental Revenue
Revenue from Contract with Customer, Excluding Assessed Tax	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
Retail Revenue [Member] | Adjustments and Eliminations
Revenue from Contract with Customer, Excluding Assessed Tax	0	0	0	0
Other non-606 revenue		0		0
Retail Revenue [Member] | Adjustments and Eliminations | Residential Revenue
Revenue from Contract with Customer, Excluding Assessed Tax	0	0	0	0
Retail Revenue [Member] | Adjustments and Eliminations | Commercial Revenue
Revenue from Contract with Customer, Excluding Assessed Tax	0	0	0	0
Retail Revenue [Member] | Adjustments and Eliminations | Industrial Revenue
Revenue from Contract with Customer, Excluding Assessed Tax	0	0	0	0
Retail Revenue [Member] | Adjustments and Eliminations | Governmental Revenue
Revenue from Contract with Customer, Excluding Assessed Tax	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

Discontinued Operations (Detail

Discontinued Operations (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Payments for Removal Costs			$ 1.2	$ 1
Disposal Group, Including Discontinued Operation, Revenue	$ 0	$ 0.9	1.4	23.3
Disposal Group, Including Discontinued Operation, Operating and Other Expenses	0	0.5	(2.4)	(23.9)
Loss from discontinued operations before income taxes	0	1.4	(1)	(0.6)
Discontinued Operation, Gain (Loss) from Disposal of Discontinued Operation, before Income Tax	0	0	0	4.5
Income tax expense / (benefit) from discontinued operations	0	0.3	(0.2)	0.8
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent	0	1.1	(0.8)	3.1
Cash Provided by (Used in) Operating Activities, Discontinued Operations	0.4	1.5	0.4	5.1
Cash Provided by (Used in) Investing Activities, Discontinued Operations	(0.4)	(0.4)	(1.2)	4
Cash flows from investing activities for discontinued operations	$ (0.4)	$ (0.4)	(1.2)	$ 4
Conesville [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Payments for Removal Costs			3
Conesville [Member] | Forecast [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Payments for Removal Costs			$ 4