Deferred Finance Costs, Net, Including Acquisition Adjustments

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Disposal Group, Including Discontinued Operations, Long-Term Debt

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Long Term Debt Maturities Repayments Of Principal, Total

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Total Long-term Debt At Subsidiary With Purchase Accounting Adjustments

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Total Maturities Before Unamortized Adjustments

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Unamortized adjustments to market value from purchase accounting

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Unamortized Deferred Financing Costs

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Unamortized Deferred Financing Costs, Consolidated

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Unamortized Deferred Financing Costs (Subsidiary)

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Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

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Contractual interest rate for funds borrowed, under the debt agreement.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Latest date the outstanding debt instruments are required to be repaid, in CCYY-MM-DD format.

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Amount, after accumulated amortization, of debt discount (premium).

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Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Amount of long-term debt and capital lease obligations including current maturities.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt, classified as current. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing after the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount after unamortized (discount) premium and debt issuance costs of long-term debt classified as noncurrent and excluding amounts to be repaid within one year or the normal operating cycle, if longer. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Debt (Long-term Debt) (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
Debt (Long-term Debt) (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018	May 07, 2019	Mar. 31, 2019	Mar. 30, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months		$ 103.6
Debt Issuance Costs, Net	$ 5.8	4.3
Disposal Group, Including Discontinued Operations, Long-Term Debt		0.0				$ (0.3)
Unamortized Deferred Financing Costs		(4.3)				(6.8)
Long-term Debt	1,362.9	1,475.9
Debt Instrument, Unamortized Discount (Premium), Net	(1.1)	(0.5)				(0.6)
Total long-term debt at subsidary		586.1				646.6
Less: current portion	(139.6)	(103.6)				(4.6)
Long-term debt, net of current portion	1,223.3	1,372.3				1,700.2
Long-term Debt, Maturities, Repayments of Principal in Year Two		144.7
Long-term Debt, Maturities, Repayments of Principal in Year Three		784.7
Long-term Debt, Maturities, Repayments of Principal in Year Four		422.8
Long-term Debt, Maturities, Repayments of Principal in Year Five		0.2
Long-term Debt, Maturities, Repayments of Principal after Year Five		32.4
Total Maturities Before Unamortized Adjustments		1,488.4
Unamortized adjustments to market value from purchase accounting		1.9
Unamortized Deferred Financing Costs, Consolidated		(10.6)
Long Term Debt Maturities Repayments Of Principal, Total		1,475.9
THE DAYTON POWER AND LIGHT COMPANY [Member]
Debt Instrument [Line Items]
Deferred Finance Costs, Net, Including Acquisition Adjustments	5.7	6.3
Unamortized Deferred Financing Costs (Subsidiary)		(6.3)				(9.8)
Debt Instrument, Unamortized Discount (Premium), Net	(2.7)	(1.4)				(2.0)
Total long-term debt at subsidary	$ 574.2	586.1
Term Loan Maturing 2022 [Domain]
Debt Instrument [Line Items]
Debt instrument maturity year	Aug. 24, 2022
Term Loan Maturing 2022 [Member] \| THE DAYTON POWER AND LIGHT COMPANY [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 0.0	436.1
Term Loan Maturing 2022 (DPL) [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross		$ 436.1				440.6
Debt instrument maturity year		Aug. 24, 2022
Tax-exempt First Mortgage Bonds - rates from: 2.49% - 2.93% (a) and 1.29% - 1.42% (b)
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 140.0	$ 140.0				200.0
Debt instrument maturity year		Aug. 01, 2020
U.S. Government note maturing in 2061 - 4.20% [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross		$ 17.7				17.8
Debt instrument maturity year	Feb. 01, 2061	Feb. 01, 2061
Debt instrument interest percentage	4.20%
U.S. Government note maturing in 2061 - 4.20% [Member] \| THE DAYTON POWER AND LIGHT COMPANY [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 17.6	$ 17.7
Senior Unsecured Notes At6.80 Maturing On October2019 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross		$ 99.0			$ 200.0
Debt instrument maturity year	Oct. 01, 2019
Debt instrument interest percentage	6.75%	6.75%		6.75%
Bank Term Loan Maturing July 2020 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross		$ 0.0				70.0
Bank Term Loan maturing in May 2018 [Member]
Debt Instrument [Line Items]
Debt instrument maturity year		Jul. 31, 2020
Five Year Senior Unsecured Notes At6.75 Maturing October152019 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross		$ 99.0				200.0
Debt instrument maturity year		Oct. 01, 2019
Debt instrument interest percentage		6.75%
Senior Unsecured Bonds at 7.25% maturing in 2021 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 380.0	$ 780.0	$ 380.0			780.0
Debt instrument maturity year	Oct. 01, 2021	Oct. 01, 2021
Debt instrument interest percentage	7.25%	7.25%		7.25%
4.35% Senior Notes due 2029 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 400.0
Debt instrument maturity year	Apr. 15, 2029
Debt instrument interest percentage	4.35%
Note to DPL Capital Trust II Maturing in 2031 - 8.125% [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 15.6	$ 15.6				$ 15.6
Debt instrument maturity year	Sep. 01, 2031	Sep. 01, 2031
Debt instrument interest percentage	8.125%	8.125%
3.95% Senior Notes due 2049 [Member] \| THE DAYTON POWER AND LIGHT COMPANY [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 425.0
Debt instrument maturity year	Jun. 15, 2049
Debt instrument interest percentage	3.95%
Variable Rate Notes Backed by Term Loan and First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Debt instrument maturity year	Aug. 01, 2020
Variable Rate Notes Backed by Term Loan and First Mortgage Bonds [Member] \| THE DAYTON POWER AND LIGHT COMPANY [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 140.0	$ 140.0
Minimum [Member] \| Term Loan Maturing 2022 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage Rate Range, Minimum (Deprecated 2016-01-31)	4.50%
Debt instrument interest percentage		4.01%
Minimum [Member] \| Term Loan Maturing 2022 (DPL) [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage Rate Range, Minimum (Deprecated 2016-01-31)		3.57%				4.00%
Minimum [Member] \| Pollution control series Maturing in 2040 - rates from: 0.02% - 0.12% and 0.04% - 0.15%
Debt Instrument [Line Items]
Debt instrument interest percentage	2.97%
Minimum [Member] \| Tax-exempt First Mortgage Bonds - rates from: 2.49% - 2.93% (a) and 1.29% - 1.42% (b)
Debt Instrument [Line Items]
Debt instrument interest percentage		2.49%				1.29%
Minimum [Member] \| Bank Term Loan maturing in May 2018 [Member]
Debt Instrument [Line Items]
Debt instrument interest percentage		3.02%				2.67%
Minimum [Member] \| Variable Rate Notes Backed by Term Loan and First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Debt instrument interest percentage		1.52%
Maximum [Member] \| Term Loan Maturing 2022 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage Rate Range, Minimum (Deprecated 2016-01-31)		4.60%
Debt instrument interest percentage	4.53%
Maximum [Member] \| Term Loan Maturing 2022 (DPL) [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage Rate Range, Minimum (Deprecated 2016-01-31)		4.82%				4.60%
Maximum [Member] \| Pollution control series Maturing in 2040 - rates from: 0.02% - 0.12% and 0.04% - 0.15%
Debt Instrument [Line Items]
Debt instrument interest percentage	3.07%
Maximum [Member] \| Tax-exempt First Mortgage Bonds - rates from: 2.49% - 2.93% (a) and 1.29% - 1.42% (b)
Debt Instrument [Line Items]
Debt instrument interest percentage		2.93%				1.42%
Maximum [Member] \| Bank Term Loan maturing in May 2018 [Member]
Debt Instrument [Line Items]
Debt instrument interest percentage		4.10%				3.02%
Maximum [Member] \| Variable Rate Notes Backed by Term Loan and First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Debt instrument interest percentage		1.92%
Debt [Member]
Debt Instrument [Line Items]
Long-term Debt and Capital Lease Obligations, Including Current Maturities		$ 1,475.9				$ 1,704.8