Debt (Narrative) (Details)						1 Months Ended	6 Months Ended	12 Months Ended
	Feb. 05, 2016 USD ($)	Aug. 03, 2015 USD ($)	Jul. 01, 2015 USD ($)	Mar. 31, 2014 USD ($)	Oct. 03, 2011 USD ($)	Oct. 31, 2014 USD ($)	Jun. 30, 2015 USD ($)	Dec. 31, 2015 USD ($) letter_of_credit fiscal_quarter debt_covenant	Dec. 31, 2014 USD ($)	Jan. 06, 2016 USD ($)	Sep. 30, 2015 fiscal_quarter debt_covenant	Jul. 31, 2015 USD ($)	Sep. 19, 2013 USD ($)
Debt Instrument [Line Items]
Additional principal amount of senior notes to be raised					$ 1,250,000,000
Current portion - long-term debt								$ 574,900,000	$ 20,100,000
Debt Covenant, Leverage Ratio, Maximum								0.67
Debt Covenant, Interest Coverage Ratio, Minimum								2.50
Leverage Ratio								1.03
THE DAYTON POWER AND LIGHT COMPANY [Member]
Debt Instrument [Line Items]
Current portion - long-term debt								$ 444,900,000	100,000
Notes payable - related party				$ 15,000,000
Revolving Credit Agreeement with Bank Group Expiring 2018 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Debt Instrument [Line Items]
Unsecured revolving credit agreement							$ 300,000,000.0
Debt Instrument, Term							5 years
Letter of credit sublimit							$ 100,000,000.0
Line of credit facility, additional borrowing capacity							100,000,000.0
Letters of credit outstanding			$ 35,300,000					1,400,000
Line of credit facility, remaining borrowing capacity								$ 173,600,000
Revolving Credit Agreement with Bank Group Expiring 2020 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Debt Instrument [Line Items]
Unsecured revolving credit agreement												$ 175,000,000.0
Letter of credit sublimit												50,000,000.0
Line of credit facility, additional borrowing capacity												100,000,000.0
Revolving Credit Agreement and Standby Letters of Credit [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Debt Instrument [Line Items]
Number of financial covenants | debt_covenant								2			2
Number of prior quarters included in debt to EBITDA ratio | fiscal_quarter								4			4
U.S. Government note maturing in 2061 - 4.20% [Member]
Debt Instrument [Line Items]
Long-term debt, gross								$ 18,100,000	18,200,000
U.S. Government note maturing in 2061 - 4.20% [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Debt Instrument [Line Items]
Debt Instrument, Maturity Date Range, End								Feb. 01, 2061
Long-term debt, gross								$ 18,100,000	18,200,000
Debt instrument interest percentage								4.20%
First Mortgage Bonds Maturing in 2016 - 1.875%
Debt Instrument [Line Items]
Long-term debt, gross								$ 445,000,000	445,000,000				$ 445,000,000
First Mortgage Bonds Maturing in 2016 - 1.875% | THE DAYTON POWER AND LIGHT COMPANY [Member]
Debt Instrument [Line Items]
Debt Instrument, Maturity Date Range, End								Sep. 01, 2016
Long-term debt, gross								$ 445,000,000	445,000,000				$ 445,000,000
Debt instrument interest percentage								1.875%
First Mortgage Bonds [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Debt Instrument [Line Items]
Repayments of debt		$ 470,000,000
Bank Term Loan maturing in May 2018 [Member]
Debt Instrument [Line Items]
Debt Instrument, Maturity Date Range, End								Jul. 31, 2020
Long-term debt, gross								$ 125,000,000	160,000,000			160,000,000
Bank Term Loan Maturing July 2020 [Member]
Debt Instrument [Line Items]
Long-term debt, gross												125,000,000
DPL Revolving Credit Facility [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Unsecured revolving credit agreement							$ 100,000,000.0					205,000,000.0
Debt Instrument, Term							5 years
Number of letters of credit outstanding | letter_of_credit								2
Letter of credit sublimit							$ 100,000,000.0					200,000,000.0
Line of credit facility, additional borrowing capacity							$ 50,000,000.0					$ 95,000,000.0
Letters of credit outstanding								$ 3,000,000
Line of credit facility, remaining borrowing capacity								$ 202,000,000
DPL Revolving Credit Agreement and Term Loan Maturing July 2020 [Member]
Debt Instrument [Line Items]
Number of financial covenants | debt_covenant								2
Debt Instrument, Debt Covenant, Debt to EBITDA Ratio, Number of Quarters | fiscal_quarter								4
Number of prior quarters included in debt to EBITDA ratio | fiscal_quarter								4
Senior Unsecured Bonds at 6.50% maturing in 2016 [Member]
Debt Instrument [Line Items]
Additional principal amount of senior notes to be raised					$ 450,000,000
Debt Instrument, Maturity Date Range, End								Oct. 01, 2016
Long-term debt, gross						$ 130,000,000		$ 130,000,000	130,000,000
Extinguishment of debt, amount						$ 300,000,000
Repayments of debt									20,000,000
Debt instrument interest percentage					6.50%	6.50%		6.50%
Senior Unsecured Bonds at 7.25% maturing in 2021 [Member]
Debt Instrument [Line Items]
Additional principal amount of senior notes to be raised					$ 800,000,000
Debt Instrument, Maturity Date Range, End								Oct. 01, 2021
Long-term debt, gross								$ 780,000,000	780,000,000
Debt instrument interest percentage					7.25%			7.25%
Senior Unsecured notes maturing October 2019 at 6.75% [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount						$ 200,000,000
Debt instrument interest percentage						6.75%
Note to DPL Capital Trust II Maturing in 2031 - 8.125% [Member]
Debt Instrument [Line Items]
Debt Instrument, Maturity Date Range, End								Sep. 01, 2031
Long-term debt, gross								$ 15,600,000	15,600,000
Repayments of debt						$ 5,000,000
Debt instrument interest percentage								8.125%
Pollution control series maturing in November 2040 - variable rates: 0.04% - 0.26% and 0.06% - 0.32% [Member]
Debt Instrument [Line Items]
Long-term debt, gross								$ 0	100,000,000
Pollution control series maturing in November 2040 - variable rates: 0.04% - 0.26% and 0.06% - 0.32% [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Debt Instrument [Line Items]
Debt Instrument, Maturity Date Range, End								Nov. 01, 2040
Long-term debt, gross								$ 0	100,000,000
Extinguishment of debt, amount		100,000,000
Pollution Control Series Maturing in 2028 - 4.70% [Member]
Debt Instrument [Line Items]
Long-term debt, gross								$ 0	35,300,000
Pollution Control Series Maturing in 2028 - 4.70% [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Debt Instrument [Line Items]
Debt Instrument, Maturity Date Range, End								Jan. 01, 2028
Long-term debt, gross								$ 0	35,300,000
Extinguishment of debt, amount			$ 35,300,000
Debt instrument interest percentage			4.70%					4.70%
Pollution Control Series Maturing in 2034 - 4.80% [Member]
Debt Instrument [Line Items]
Long-term debt, gross								$ 0	179,100,000
Pollution Control Series Maturing in 2034 - 4.80% [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Debt Instrument [Line Items]
Debt Instrument, Maturity Date Range, End								Jan. 01, 2034
Long-term debt, gross								$ 0	$ 179,100,000
Extinguishment of debt, amount		137,800,000	$ 41,300,000
Repayments of debt		$ 37,800,000
Debt instrument interest percentage		4.80%	4.80%					4.80%
Note Payable to DPL Inc. [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Debt Instrument [Line Items]
Debt instrument interest percentage								2.67%
Notes payable - related party								$ 35,000,000
Variable Rate Notes Backed by Term Loan and First Mortgage Bonds [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount		$ 200,000,000.0
Subsequent Event [Member] | Senior Unsecured Bonds at 6.50% maturing in 2016 [Member]
Debt Instrument [Line Items]
Long-term debt, gross										$ 130,000,000
Make Whole Premium	$ 2,400,000
Extinguishment of debt, amount	$ 73,000,000
Debt instrument interest percentage										6.50%
London Interbank Offered Rate (LIBOR) [Member] | Note Payable to DPL Inc. [Member]
Debt Instrument [Line Items]
Basis spread on variable interest rate (percent)				2.00%