Benefit Plans (Tables)

12 Months Ended

Dec. 31, 2023

Defined Benefit Plan, Plan Assets, Category

The fair values of our Pension Plans' assets at December 31, 2023 by asset category are as follows:

$ in millions	Market Value at December 31, 2023		Quoted prices in active markets for identical assets		Significant observable inputs		Significant unobservable inputs
Asset category			(Level 1)		(Level 2)		(Level 3)
Common collective trusts
Equities (a)	$	84.5	$	—	$	84.5	$	—
Debt securities (b)	121.1		—		121.1		—
Government debt securities (c)	61.0		—		61.0		—
Total common collective trusts	266.6		—		266.6		—
Cash and cash equivalents (d)	1.8		1.8		—		—
Total pension plan assets	$	268.4	$	1.8	$	266.6	$	—

(a)    This category represents investments that invest in equity securities of U.S. companies of any market capitalization and other investments (i.e.: futures, swaps, currency forwards) of foreign, emerging markets and seeks to provide long-term total return, which includes capital appreciation and income. The funds are valued using the net asset value method.

(b)    This category represents investments that invest in high quality issues within the U.S. corporate bond markets and global high yield bonds and emerging markets debt denominated in local currency. The funds seek to provide current income and long-term capital preservation along with access to higher yielding, relatively liquid fixed income securities. The funds are valued using the net asset value method.

(c)    This category represents investments that invest in U.S. treasury strips, U.S. government agency obligations, and U.S. treasury obligations. The funds seek investment returns over the long term and are valued using the net asset value method.

(d)    This category represents an investment that seeks to maximize current income on cash reserves to the extent consistent with principal preservation and maintenance of liquidity from a portfolio of obligations of the U.S. Government, its agencies or municipalities, and related money market instruments. Principal preservation is a primary objective. The fund is valued at cost.

The fair values of our pension plan assets at December 31, 2022 by asset category are as follows:

$ in millions	Market Value at December 31, 2022		Quoted prices in active markets for identical assets		Significant observable inputs		Significant unobservable inputs
Asset category			(Level 1)		(Level 2)		(Level 3)
Common collective trusts
Equities (a)	$	88.5	$	—	$	88.5	$	—
Debt securities (b)	125.7		—		125.7		—
Government debt securities (c)	58.3		—		58.3		—
Total common collective trusts	272.5		—		272.5		—
Cash and cash equivalents (d)	1.9		1.9		—		—
Total pension plan assets	$	274.4	$	1.9	$	272.5	$	—

(a)    This category represents investments that invest in equity securities of U.S. companies of any market capitalization and other investments (i.e.: futures, swaps, currency forwards) of foreign, emerging markets and seeks to provide long-term total return, which includes capital appreciation and income. The funds are valued using the net asset value method.

(b)    This category represents investments that invest in high quality issues within the U.S. corporate bond markets and global high yield bonds and emerging markets debt denominated in local currency. The funds seek to provide current income and long-term capital preservation along with access to higher yielding, relatively liquid fixed income securities. The funds are valued using the net asset value method.

(c)    This category represents investments that invest in U.S. treasury strips, U.S. government agency obligations, and U.S. treasury obligations. The funds seek investment returns over the long term and are valued using the net asset value method.

(d)    This category represents an investment that seeks to maximize current income on cash reserves to the extent consistent with principal preservation and maintenance of liquidity from a portfolio of obligations of the U.S. Government, its agencies or municipalities, and related money market instruments. Principal preservation is a primary objective. The fund is valued at cost.

Pension And Postretirement Benefit Plans' Obligations And Assets

The following tables set forth the changes in the Pension Plans' obligations and assets recorded on the Consolidated Balance Sheets at December 31, 2023 and 2022. The amounts presented in the following tables for pension obligations include the collective bargaining plan formula, traditional management plan formula and cash balance plan formula and the SERP in the aggregate and have not been adjusted for $0.9 million, $1.7 million and $1.7 million of costs billed to the Service Company for the years ended December 31, 2023, 2022 and 2021, respectively.

$ in millions	Years ended December 31,
Change in benefit obligation	2023		2022
Benefit obligation at January 1	$	309.0	$	416.2
Service cost	3.0		4.9
Interest cost	15.8		9.6
Plan amendments	1.4		—
Actuarial loss / (gain)	9.6		(98.0)
Benefits paid	(40.2)		(23.7)
Benefit obligation at December 31	298.6		309.0
Change in plan assets
Fair value of plan assets at January 1	274.4		363.5
Actual return / (loss) on plan assets	26.5		(73.1)
Employer contributions	7.7		7.7
Benefits paid	(40.2)		(23.7)
Fair value of plan assets at December 31	268.4		274.4
Unfunded status of plan	$	(30.2)	$	(34.6)
	December 31,
Amounts recognized in the Consolidated Balance Sheets	2023		2022
Current liabilities	$	(0.2)	$	(0.2)
Non-current liabilities	(30.0)		(34.4)
Net liability at end of year	$	(30.2)	$	(34.6)
Amounts recognized in Accumulated other comprehensive loss, Regulatory assets, non-current, pre-tax
Components:
Prior service cost	$	7.7	$	7.3
Net actuarial loss	78.7		78.6
Accumulated other comprehensive loss, Regulatory assets, pre-tax	$	86.4	$	85.9
Recorded in:
Regulatory asset, non-current	$	60.7	$	62.0
Accumulated other comprehensive loss	25.7		23.9
Accumulated other comprehensive loss, Regulatory assets, pre-tax	$	86.4	$	85.9

Schedule of Net Periodic Benefit Cost / (Income)

The net periodic benefit cost of the Pension Plans was:

	Years ended December 31,
$ in millions	2023			2022			2021
Service cost	$	3.0		$	4.9		$	4.5
Interest cost	15.8			9.6			8.2
Expected return on assets	(17.6)			(15.8)			(15.0)
Amortization of unrecognized:
Actuarial loss	0.6			5.5			9.0
Prior service cost	1.0			1.1			0.9
Net periodic benefit cost	$	2.8		$	5.3		$	7.6
Rates relevant to each year's expense calculations
Discount rate	5.41		%	2.83		%	2.44		%
Expected return on plan assets	5.40		%	4.60		%	4.55		%

Schedule of Allocation of Plan Assets

The following table summarizes our target pension plan allocation:

	Long-Term Mid-Point Target Allocation	Percentage of plan assets as of December 31,
Asset category		2023	2022
Equity Securities	32%	32%	32%
Debt Securities	68%	67%	67%
Cash and Cash Equivalents	—%	1%	1%

Other Changes in Plan Assets and Benefit Obligation Recognized in Accumulated Other Comprehensive Income, Regulatory Assets And Regulatory Liabilities

The following table presents other changes in Pension Plan assets and benefit obligations recognized in Accumulated other comprehensive loss, Regulatory assets, non-current and Regulatory liabilities, non-current:

	Years ended December 31,
$ in millions	2023		2022		2021
Net actuarial loss / (gain)	$	0.7	$	(9.1)	$	(21.7)
Plan amendments	1.4		—		2.3
Reversal of amortization item:
Net actuarial loss	(0.6)		(5.5)		(9.0)
Prior service cost	(1.0)		(1.1)		(0.9)
Total recognized in Accumulated other comprehensive loss, Regulatory assets and Regulatory liabilities	$	0.5	$	(15.7)	$	(29.3)
Total recognized in net periodic benefit cost and Accumulated other comprehensive loss, Regulatory assets and Regulatory liabilities	$	3.3	$	(10.4)	$	(21.7)

Weighted Average Assumptions Used to Determine Benefit Obligations

The weighted average assumptions used to determine benefit obligations were:

Benefit Obligation Assumptions	Pension
	2023	2022	2021
Discount rate for obligations	5.14%	5.41%	2.83%
Rate of compensation increases	3.21%	3.21%	3.21%

Estimated Future Benefit Payments and Medicare Part D Reimbursements

Benefit payments, which reflect future service, are expected to be paid as follows:

Estimated future benefit payments
$ in millions due within the following years:	Pension
2024	$	22.4
2025	22.1
2026	22.1
2027	21.9
2028	21.8
2029 - 2033	106.7

Schedule of Unrecognized Tax Benefits Roll Forward

$ in millions	2023		2022		2021
Unrecognized tax benefits at January 1	$	0.4	$	0.4	$	1.4
Gross decreases - prior period tax positions	—		—		(1.0)
Unrecognized tax benefits at December 31	$	0.4	$	0.4	$	0.4

Fair Value, Liabilities Measured on Recurring and Nonrecurring Basis

The following table presents the carrying amount, fair value, and fair value hierarchy of our financial liabilities that are not measured at fair value in the Consolidated Balance Sheets as of the periods indicated, but for which fair value is disclosed:

	Carrying Amount		Fair Value at December 31, 2023								Carrying Amount		Fair Value at December 31, 2022
$ in millions			Level 1		Level 2		Level 3		Total				Level 1		Level 2		Level 3		Total
Liabilities
Long-term debt	$	1,837.6	$	—	$	1,706.2	$	16.8	$	1,723.0	$	1,535.9	$	—	$	1,376.4	$	17.0	$	1,393.4

Fair Value, Assets Measured on Recurring Basis

The fair value of assets at December 31, 2023 and 2022 and the respective category within the fair value hierarchy for DPL was determined as follows:

$ in millions	Fair Value at December 31, 2023								Fair Value at December 31, 2022
	Level 1		Level 2		Level 3		Total		Level 1		Level 2		Level 3		Total
Assets
Master trust assets
Money market funds	$	0.6	$	—	$	—	$	0.6	$	0.5	$	—	$	—	$	0.5
Mutual funds	7.2		—		—		7.2		7.0		—		—		7.0
Total assets	$	7.8	$	—	$	—	$	7.8	$	7.5	$	—	$	—	$	7.5

THE DAYTON POWER AND LIGHT COMPANY [Member]

Schedule of Net Periodic Benefit Cost / (Income)

	Years ended December 31,
$ in millions	2023			2022			2021
Service cost	$	3.0		$	4.9		$	4.5
Interest cost	15.8			9.6			8.2
Expected return on assets	(17.6)			(15.8)			(15.0)
Amortization of unrecognized:
Actuarial loss	1.1			7.7			11.4
Prior service cost	1.1			1.2			1.1
Net periodic benefit cost	$	3.4		$	7.6		$	10.2
Rates relevant to each year's expense calculations
Discount rate	5.41		%	2.83		%	2.44		%
Expected return on plan assets	5.40		%	4.60		%	4.55		%

Schedule of Allocation of Plan Assets

The following table summarizes our target pension plan allocation:

	Long-Term Mid-Point Target Allocation	Percentage of plan assets as of December 31,
Asset category		2023	2022
Equity Securities	32%	32%	32%
Debt Securities	68%	67%	67%
Cash and Cash Equivalents	—%	1%	1%

Weighted Average Assumptions Used to Determine Benefit Obligations

The weighted average assumptions used to determine benefit obligations were:

Benefit Obligation Assumptions	Pension
	2023	2022	2021
Discount rate for obligations	5.14%	5.41%	2.83%
Rate of compensation increases	3.21%	3.21%	3.21%

Estimated Future Benefit Payments and Medicare Part D Reimbursements

Benefit payments, which reflect future service, are expected to be paid as follows:

Estimated future benefit payments
$ in millions due within the following years:	Pension
2024	$	22.4
2025	22.1
2026	22.1
2027	21.9
2028	21.8
2029 - 2033	106.7

Schedule of Unrecognized Tax Benefits Roll Forward

$ in millions	2023		2022		2021
Unrecognized tax benefits at January 1	$	0.4	$	0.4	$	1.4
Gross decreases - prior period tax positions	—		—		(1.0)
Unrecognized tax benefits at December 31	$	0.4	$	0.4	$	0.4

Fair Value, Liabilities Measured on Recurring and Nonrecurring Basis

The following table presents the carrying amount, fair value, and fair value hierarchy of our financial liabilities that are not measured at fair value in the Balance Sheets as of the periods indicated, but for which fair value is disclosed:

	Carrying Amount		Fair Value at December 31, 2023								Carrying Amount		Fair Value at December 31, 2022
$ in millions			Level 1		Level 2		Level 3		Total				Level 1		Level 2		Level 3		Total
Liabilities
Long-term debt	$	1,012.5	$	—	$	909.9	$	16.8	$	926.7	$	712.7	$	—	$	610.9	$	17.0	$	627.9

Fair Value, Assets Measured on Recurring Basis

The fair value of assets at December 31, 2023 and 2022 and the respective category within the fair value hierarchy for AES Ohio was determined as follows:

$ in millions	Fair Value at December 31, 2023								Fair Value at December 31, 2022
	Level 1		Level 2		Level 3		Total		Level 1		Level 2		Level 3		Total
Assets
Money market funds	$	0.6	$	—	$	—	$	0.6	$	0.5	$	—	$	—	$	0.5
Mutual funds	7.2		—		—		7.2		7.0		—		—		7.0
Total assets	$	7.8	$	—	$	—	$	7.8	$	7.5	$	—	$	—	$	7.5

Pension [Member]

Pension And Postretirement Benefit Plans' Obligations And Assets

The following tables set forth the changes in the Pension Plans' obligations and assets recorded on the Consolidated Balance Sheets at December 31, 2023 and 2022. The amounts presented in the following tables for pension obligations include the collective bargaining plan formula, traditional management plan formula and cash balance plan formula and the SERP in the aggregate and have not been adjusted for $0.9 million, $1.7 million and $1.7 million of costs billed to the Service Company for the years ended December 31, 2023, 2022 and 2021, respectively.

$ in millions	Years ended December 31,
Change in benefit obligation	2023		2022
Benefit obligation at January 1	$	309.0	$	416.2
Service cost	3.0		4.9
Interest cost	15.8		9.6
Plan amendments	1.4		—
Actuarial loss / (gain)	9.6		(98.0)
Benefits paid	(40.2)		(23.7)
Benefit obligation at December 31	298.6		309.0
Change in plan assets
Fair value of plan assets at January 1	274.4		363.5
Actual return / (loss) on plan assets	26.5		(73.1)
Employer contributions	7.7		7.7
Benefits paid	(40.2)		(23.7)
Fair value of plan assets at December 31	268.4		274.4
Unfunded status of plan	$	(30.2)	$	(34.6)
	December 31,
Amounts recognized in the Consolidated Balance Sheets	2023		2022
Current liabilities	$	(0.2)	$	(0.2)
Non-current liabilities	(30.0)		(34.4)
Net liability at end of year	$	(30.2)	$	(34.6)
Amounts recognized in Accumulated other comprehensive loss, Regulatory assets, non-current, pre-tax
Components:
Prior service cost	$	7.7	$	7.3
Net actuarial loss	78.7		78.6
Accumulated other comprehensive loss, Regulatory assets, pre-tax	$	86.4	$	85.9
Recorded in:
Regulatory asset, non-current	$	60.7	$	62.0
Accumulated other comprehensive loss	25.7		23.9
Accumulated other comprehensive loss, Regulatory assets, pre-tax	$	86.4	$	85.9

Fair Value Measurements for Plan Assets

The fair values of our Pension Plans' assets at December 31, 2023 by asset category are as follows:

$ in millions	Market Value at December 31, 2023		Quoted prices in active markets for identical assets		Significant observable inputs		Significant unobservable inputs
Asset category			(Level 1)		(Level 2)		(Level 3)
Common collective trusts
Equities (a)	$	84.5	$	—	$	84.5	$	—
Debt securities (b)	121.1		—		121.1		—
Government debt securities (c)	61.0		—		61.0		—
Total common collective trusts	266.6		—		266.6		—
Cash and cash equivalents (d)	1.8		1.8		—		—
Total pension plan assets	$	268.4	$	1.8	$	266.6	$	—

(a)    This category represents investments that invest in equity securities of U.S. companies of any market capitalization and other investments (i.e.: futures, swaps, currency forwards) of foreign, emerging markets and seeks to provide long-term total return, which includes capital appreciation and income. The funds are valued using the net asset value method.

(b)    This category represents investments that invest in high quality issues within the U.S. corporate bond markets and global high yield bonds and emerging markets debt denominated in local currency. The funds seek to provide current income and long-term capital preservation along with access to higher yielding, relatively liquid fixed income securities. The funds are valued using the net asset value method.

(c)    This category represents investments that invest in U.S. treasury strips, U.S. government agency obligations, and U.S. treasury obligations. The funds seek investment returns over the long term and are valued using the net asset value method.

(d)    This category represents an investment that seeks to maximize current income on cash reserves to the extent consistent with principal preservation and maintenance of liquidity from a portfolio of obligations of the U.S. Government, its agencies or municipalities, and related money market instruments. Principal preservation is a primary objective. The fund is valued at cost.

The fair values of our Pension Plans' assets at December 31, 2022 by asset category are as follows:

$ in millions	Market Value at December 31, 2022		Quoted prices in active markets for identical assets		Significant observable inputs		Significant unobservable inputs
Asset category			(Level 1)		(Level 2)		(Level 3)
Common collective trusts
Equities (a)	$	88.5	$	—	$	88.5	$	—
Debt securities (b)	125.7		—		125.7		—
Government debt securities (c)	58.3		—		58.3		—
Total common collective trusts	272.5		—		272.5		—
Cash and cash equivalents (d)	1.9		1.9		—		—
Total pension plan assets	$	274.4	$	1.9	$	272.5	$	—

(a)    This category represents investments that invest in equity securities of U.S. companies of any market capitalization and other investments (i.e.: futures, swaps, currency forwards) of foreign, emerging markets and seeks to provide long-term total return, which includes capital appreciation and income. The funds are valued using the net asset value method.

(b)    This category represents investments that invest in high quality issues within the U.S. corporate bond markets and global high yield bonds and emerging markets debt denominated in local currency. The funds seek to provide current income and long-term capital preservation along with access to higher yielding, relatively liquid fixed income securities. The funds are valued using the net asset value method.

(c)    This category represents investments that invest in U.S. treasury strips, U.S. government agency obligations, and U.S. treasury obligations. The funds seek investment returns over the long term and are valued using the net asset value method.

(d)    This category represents an investment that seeks to maximize current income on cash reserves to the extent consistent with principal preservation and maintenance of liquidity from a portfolio of obligations of the U.S. Government, its agencies or municipalities, and related money market instruments. Principal preservation is a primary objective. The fund is valued at cost.

Pension [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]

Pension And Postretirement Benefit Plans' Obligations And Assets

The following tables set forth the changes in the Pension Plans' obligations and assets recorded on the Balance Sheets at December 31, 2023 and 2022. The amounts presented in the following tables for pension obligations include the collective bargaining plan formula, traditional management plan formula and cash balance plan formula and the SERP in the aggregate and have not been adjusted for $0.9 million, $1.7 million and $1.7 million of costs billed to the Service Company for the years ended December 31, 2023, 2022 and 2021, respectively, or $0.2 million, $0.9 million and $1.9 million of costs billed to AES Ohio Generation for the years ended December 31, 2023, 2022 and 2021, respectively.

$ in millions	Years ended December 31,
Change in benefit obligation	2023		2022
Benefit obligation at January 1	$	309.0	$	416.2
Service cost	3.0		4.9
Interest cost	15.8		9.6
Plan amendments	1.4		—
Actuarial loss / (gain)	9.6		(98.0)
Benefits paid	(40.2)		(23.7)
Benefit obligation at December 31	298.6		309.0
Change in plan assets
Fair value of plan assets at January 1	274.4		363.5
Actual return / (loss) on plan assets	26.5		(73.1)
Employer contributions	7.7		7.7
Benefits paid	(40.2)		(23.7)
Fair value of plan assets at December 31	268.4		274.4
Unfunded status of plan	$	(30.2)	$	(34.6)
	December 31,
Amounts recognized in the Balance Sheets	2023		2022
Current liabilities	$	(0.2)	$	(0.2)
Non-current liabilities	(30.0)		(34.4)
Net liability at end of year	$	(30.2)	$	(34.6)
Amounts recognized in Accumulated other comprehensive loss, Regulatory assets, non-current, pre-tax
Components:
Prior service cost	$	7.6	$	7.3
Net actuarial loss	102.3		102.7
Accumulated other comprehensive loss, Regulatory assets, pre-tax	$	109.9	$	110.0
Recorded in:
Regulatory assets, non-current	$	60.7	$	62.0
Accumulated other comprehensive loss	49.2		48.0
Accumulated other comprehensive loss, Regulatory assets, pre-tax	$	109.9	$	110.0

Other Changes in Plan Assets and Benefit Obligation Recognized in Accumulated Other Comprehensive Income, Regulatory Assets And Regulatory Liabilities

	Years ended December 31,
$ in millions	2023		2022		2021
Net actuarial loss / (gain)	$	0.7	$	(9.1)	$	(21.7)
Plan amendments	1.4		—		2.3
Reversal of amortization item:
Net actuarial loss	(1.1)		(7.7)		(11.4)
Prior service cost	(1.1)		(1.2)		(1.1)
Total recognized in Accumulated other comprehensive loss, Regulatory assets and Regulatory liabilities	$	(0.1)	$	(18.0)	$	(31.9)
Total recognized in net periodic benefit cost and Accumulated other comprehensive loss, Regulatory assets and Regulatory liabilities	$	3.3	$	(10.4)	$	(21.7)