Derivative Instruments and Hedging Activities (Fair Value and Balance Sheet Location (Details) - USD ($) $ in Millions | Jun. 30, 2017 | Dec. 31, 2016 |
Derivative Liability, Fair Value | $ 11.6 | |
Liability position offset by the asset position of counterparties with master netting agreements | 9.4 | |
THE DAYTON POWER AND LIGHT COMPANY [Member] | | |
Derivative Liability, Fair Value | 11.6 | |
Liability position offset by the asset position of counterparties with master netting agreements | 9.4 | |
Total Assets [Member] | | |
Derivative Asset, Fair Value | 17.6 | $ 20.8 |
Derivative, Collateral, Obligation to Return Securities | (9.4) | (16.8) |
Derivative, Collateral, Obligation to Return Cash | 0 | 0 |
Derivative Asset, Fair Value, Amount Offset Against Collateral | 8.2 | 4 |
Total Assets [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | | |
Derivative Asset, Fair Value | 17.6 | 20.8 |
Derivative, Collateral, Obligation to Return Securities | (9.4) | (16.8) |
Derivative, Collateral, Obligation to Return Cash | 0 | 0 |
Derivative Asset, Fair Value, Amount Offset Against Collateral | 8.2 | 4 |
Total Liabilities [Member] | | |
Derivative Liability, Fair Value | 11.6 | 29.2 |
Derivative, Collateral, Right to Reclaim Securities | (9.4) | (16.8) |
Derivative, Collateral, Right to Reclaim Cash | (0.8) | (6.3) |
Liability position offset by the asset position of counterparties with master netting agreements | 1.4 | 6.1 |
Total Liabilities [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | | |
Derivative Liability, Fair Value | 11.6 | 29.2 |
Derivative, Collateral, Right to Reclaim Securities | (9.4) | (16.8) |
Derivative, Collateral, Right to Reclaim Cash | (0.8) | (6.3) |
Liability position offset by the asset position of counterparties with master netting agreements | 1.4 | 6.1 |
Cash Flow Hedging [Member] | Forward Contract Power [Member] | Short-term Derivative Positions [Member] | Other Prepayments and Current Assets [Member] | | |
Derivative Asset, Fair Value | 10.2 | 11 |
Derivative, Collateral, Obligation to Return Securities | (5) | (10.5) |
Derivative, Collateral, Obligation to Return Cash | 0 | 0 |
Derivative Asset, Fair Value, Amount Offset Against Collateral | 5.2 | 0.5 |
Cash Flow Hedging [Member] | Forward Contract Power [Member] | Short-term Derivative Positions [Member] | Other Prepayments and Current Assets [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | | |
Derivative Asset, Fair Value | 10.2 | 11 |
Derivative, Collateral, Obligation to Return Securities | (5) | (10.5) |
Derivative, Collateral, Obligation to Return Cash | 0 | 0 |
Derivative Asset, Fair Value, Amount Offset Against Collateral | 5.2 | 0.5 |
Cash Flow Hedging [Member] | Forward Contract Power [Member] | Short-term Derivative Positions [Member] | Other Current Liabilities [Member] | | |
Derivative Liability, Fair Value | 5.3 | 16.4 |
Derivative, Collateral, Right to Reclaim Securities | (5) | (10.5) |
Derivative, Collateral, Right to Reclaim Cash | 0 | (5.5) |
Liability position offset by the asset position of counterparties with master netting agreements | 0.3 | 0.4 |
Cash Flow Hedging [Member] | Forward Contract Power [Member] | Short-term Derivative Positions [Member] | Other Current Liabilities [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | | |
Derivative Liability, Fair Value | 5.3 | 16.4 |
Derivative, Collateral, Right to Reclaim Securities | (5) | (10.5) |
Derivative, Collateral, Right to Reclaim Cash | 0 | (5.5) |
Liability position offset by the asset position of counterparties with master netting agreements | 0.3 | 0.4 |
Cash Flow Hedging [Member] | Forward Contract Power [Member] | Long-term Derivative Positions [Member] | Other Deferred Asset [Member] | | |
Derivative Asset, Fair Value | | 0.6 |
Derivative, Collateral, Obligation to Return Securities | | (0.6) |
Derivative, Collateral, Obligation to Return Cash | | 0 |
Derivative Asset, Fair Value, Amount Offset Against Collateral | | 0 |
Cash Flow Hedging [Member] | Forward Contract Power [Member] | Long-term Derivative Positions [Member] | Other Deferred Asset [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | | |
Derivative Asset, Fair Value | | 0.6 |
Derivative, Collateral, Obligation to Return Securities | | (0.6) |
Derivative, Collateral, Obligation to Return Cash | | 0 |
Derivative Asset, Fair Value, Amount Offset Against Collateral | | 0 |
Cash Flow Hedging [Member] | Forward Contract Power [Member] | Long-term Derivative Positions [Member] | Other Deferred Credit [Member] | | |
Derivative Liability, Fair Value | | 2.4 |
Derivative, Collateral, Right to Reclaim Securities | | (0.6) |
Derivative, Collateral, Right to Reclaim Cash | | (0.8) |
Liability position offset by the asset position of counterparties with master netting agreements | | 1 |
Cash Flow Hedging [Member] | Forward Contract Power [Member] | Long-term Derivative Positions [Member] | Other Deferred Credit [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | | |
Derivative Liability, Fair Value | | 2.4 |
Derivative, Collateral, Right to Reclaim Securities | | (0.6) |
Derivative, Collateral, Right to Reclaim Cash | | (0.8) |
Liability position offset by the asset position of counterparties with master netting agreements | | 1 |
Cash Flow Hedging [Member] | Natural Gas Futures [Member] | Long-term Derivative Positions [Member] | Other Deferred Asset [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | | |
Derivative Asset, Fair Value | 0.2 | |
Derivative, Collateral, Obligation to Return Securities | (0.2) | |
Derivative, Collateral, Obligation to Return Cash | 0 | |
Derivative Asset, Fair Value, Amount Offset Against Collateral | 0 | |
Cash Flow Hedging [Member] | Interest Rate Swap [Member] | Short-term Derivative Positions [Member] | Other Current Liabilities [Member] | | |
Derivative Liability, Fair Value | | 0.7 |
Derivative, Collateral, Right to Reclaim Securities | | 0 |
Derivative, Collateral, Right to Reclaim Cash | | 0 |
Liability position offset by the asset position of counterparties with master netting agreements | | 0.7 |
Cash Flow Hedging [Member] | Interest Rate Swap [Member] | Short-term Derivative Positions [Member] | Other Current Liabilities [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | | |
Derivative Liability, Fair Value | | 0.7 |
Derivative, Collateral, Right to Reclaim Securities | | 0 |
Derivative, Collateral, Right to Reclaim Cash | | 0 |
Liability position offset by the asset position of counterparties with master netting agreements | | 0.7 |
Cash Flow Hedging [Member] | Interest Rate Swap [Member] | Long-term Derivative Positions [Member] | Other Deferred Asset [Member] | | |
Derivative Asset, Fair Value | 0.9 | 1.2 |
Derivative, Collateral, Obligation to Return Securities | 0 | 0 |
Derivative, Collateral, Obligation to Return Cash | 0 | 0 |
Derivative Asset, Fair Value, Amount Offset Against Collateral | 0.9 | 1.2 |
Cash Flow Hedging [Member] | Interest Rate Swap [Member] | Long-term Derivative Positions [Member] | Other Deferred Asset [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | | |
Derivative Asset, Fair Value | 0.9 | 1.2 |
Derivative, Collateral, Obligation to Return Securities | 0 | 0 |
Derivative, Collateral, Obligation to Return Cash | 0 | 0 |
Derivative Asset, Fair Value, Amount Offset Against Collateral | 0.9 | 1.2 |
Fair Value Hedging [Member] | Commodity Contract - FTR [Member] | Short-term Derivative Positions [Member] | Other Prepayments and Current Assets [Member] | | |
Derivative Asset, Fair Value | | 0.1 |
Derivative, Collateral, Obligation to Return Securities | | 0 |
Derivative, Collateral, Obligation to Return Cash | | 0 |
Derivative Asset, Fair Value, Amount Offset Against Collateral | | 0.1 |
Fair Value Hedging [Member] | Commodity Contract - FTR [Member] | Short-term Derivative Positions [Member] | Other Prepayments and Current Assets [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | | |
Derivative Asset, Fair Value | | 0.1 |
Derivative, Collateral, Obligation to Return Securities | | 0 |
Derivative, Collateral, Obligation to Return Cash | | 0 |
Derivative Asset, Fair Value, Amount Offset Against Collateral | | 0.1 |
Fair Value Hedging [Member] | Commodity Contract - FTR [Member] | Short-term Derivative Positions [Member] | Other Current Liabilities [Member] | | |
Derivative Liability, Fair Value | 0.6 | |
Derivative, Collateral, Right to Reclaim Securities | 0 | |
Derivative, Collateral, Right to Reclaim Cash | 0 | |
Liability position offset by the asset position of counterparties with master netting agreements | 0.6 | |
Fair Value Hedging [Member] | Commodity Contract - FTR [Member] | Short-term Derivative Positions [Member] | Other Current Liabilities [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | | |
Derivative Liability, Fair Value | 0.6 | |
Derivative, Collateral, Right to Reclaim Securities | 0 | |
Derivative, Collateral, Right to Reclaim Cash | 0 | |
Liability position offset by the asset position of counterparties with master netting agreements | 0.6 | |
Fair Value Hedging [Member] | Natural Gas [Member] | Short-term Derivative Positions [Member] | Other Current Liabilities [Member] | | |
Derivative Liability, Fair Value | 0.7 | |
Derivative, Collateral, Right to Reclaim Securities | 0 | |
Derivative, Collateral, Right to Reclaim Cash | (0.7) | |
Liability position offset by the asset position of counterparties with master netting agreements | 0 | |
Fair Value Hedging [Member] | Natural Gas [Member] | Short-term Derivative Positions [Member] | Other Current Liabilities [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | | |
Derivative Liability, Fair Value | 0.7 | |
Derivative, Collateral, Right to Reclaim Securities | 0 | |
Derivative, Collateral, Right to Reclaim Cash | (0.7) | |
Liability position offset by the asset position of counterparties with master netting agreements | 0 | |
Fair Value Hedging [Member] | Forward Contract Power [Member] | Short-term Derivative Positions [Member] | Other Prepayments and Current Assets [Member] | | |
Derivative Asset, Fair Value | 5.1 | 6 |
Derivative, Collateral, Obligation to Return Securities | (4.2) | (4.7) |
Derivative, Collateral, Obligation to Return Cash | 0 | 0 |
Derivative Asset, Fair Value, Amount Offset Against Collateral | 0.9 | 1.3 |
Fair Value Hedging [Member] | Forward Contract Power [Member] | Short-term Derivative Positions [Member] | Other Prepayments and Current Assets [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | | |
Derivative Asset, Fair Value | 5.1 | 6 |
Derivative, Collateral, Obligation to Return Securities | (4.2) | (4.7) |
Derivative, Collateral, Obligation to Return Cash | 0 | 0 |
Derivative Asset, Fair Value, Amount Offset Against Collateral | 0.9 | 1.3 |
Fair Value Hedging [Member] | Forward Contract Power [Member] | Short-term Derivative Positions [Member] | Other Current Liabilities [Member] | | |
Derivative Liability, Fair Value | 4.5 | 7.7 |
Derivative, Collateral, Right to Reclaim Securities | (4.2) | (4.7) |
Derivative, Collateral, Right to Reclaim Cash | 0 | 0 |
Liability position offset by the asset position of counterparties with master netting agreements | 0.3 | 3 |
Fair Value Hedging [Member] | Forward Contract Power [Member] | Short-term Derivative Positions [Member] | Other Current Liabilities [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | | |
Derivative Liability, Fair Value | 4.5 | 7.7 |
Derivative, Collateral, Right to Reclaim Securities | (4.2) | (4.7) |
Derivative, Collateral, Right to Reclaim Cash | 0 | 0 |
Liability position offset by the asset position of counterparties with master netting agreements | 0.3 | 3 |
Fair Value Hedging [Member] | Forward Contract Power [Member] | Long-term Derivative Positions [Member] | Other Deferred Asset [Member] | | |
Derivative Asset, Fair Value | 1.1 | 1.9 |
Derivative, Collateral, Obligation to Return Securities | 0 | (1) |
Derivative, Collateral, Obligation to Return Cash | 0 | 0 |
Derivative Asset, Fair Value, Amount Offset Against Collateral | 1.1 | 0.9 |
Fair Value Hedging [Member] | Forward Contract Power [Member] | Long-term Derivative Positions [Member] | Other Deferred Asset [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | | |
Derivative Asset, Fair Value | 1.1 | 1.9 |
Derivative, Collateral, Obligation to Return Securities | 0 | (1) |
Derivative, Collateral, Obligation to Return Cash | 0 | 0 |
Derivative Asset, Fair Value, Amount Offset Against Collateral | 1.1 | 0.9 |
Fair Value Hedging [Member] | Forward Contract Power [Member] | Long-term Derivative Positions [Member] | Other Deferred Credit [Member] | | |
Derivative Liability, Fair Value | | 2 |
Derivative, Collateral, Right to Reclaim Securities | | (1) |
Derivative, Collateral, Right to Reclaim Cash | | 0 |
Liability position offset by the asset position of counterparties with master netting agreements | | 1 |
Fair Value Hedging [Member] | Forward Contract Power [Member] | Long-term Derivative Positions [Member] | Other Deferred Credit [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | | |
Derivative Liability, Fair Value | | 2 |
Derivative, Collateral, Right to Reclaim Securities | | (1) |
Derivative, Collateral, Right to Reclaim Cash | | 0 |
Liability position offset by the asset position of counterparties with master netting agreements | | $ 1 |
Fair Value Hedging [Member] | Natural Gas Futures [Member] | Short-term Derivative Positions [Member] | Other Prepayments and Current Assets [Member] | | |
Derivative Asset, Fair Value | 0.1 | |
Derivative, Collateral, Obligation to Return Securities | 0 | |
Derivative, Collateral, Obligation to Return Cash | 0 | |
Derivative Asset, Fair Value, Amount Offset Against Collateral | 0.1 | |
Fair Value Hedging [Member] | Natural Gas Futures [Member] | Short-term Derivative Positions [Member] | Other Prepayments and Current Assets [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | | |
Derivative Asset, Fair Value | 0.1 | |
Derivative, Collateral, Obligation to Return Securities | 0 | |
Derivative, Collateral, Obligation to Return Cash | 0 | |
Derivative Asset, Fair Value, Amount Offset Against Collateral | 0.1 | |
Fair Value Hedging [Member] | Natural Gas Futures [Member] | Long-term Derivative Positions [Member] | Other Deferred Asset [Member] | | |
Derivative Asset, Fair Value | 0.2 | |
Derivative, Collateral, Obligation to Return Securities | (0.2) | |
Derivative, Collateral, Obligation to Return Cash | 0 | |
Derivative Asset, Fair Value, Amount Offset Against Collateral | 0 | |
Designated as Hedging Instrument [Member] | Interest Rate Swap [Member] | Short-term Derivative Positions [Member] | Other Current Liabilities [Member] | | |
Derivative Liability, Fair Value | 0.2 | |
Derivative, Collateral, Right to Reclaim Securities | 0 | |
Derivative, Collateral, Right to Reclaim Cash | 0 | |
Liability position offset by the asset position of counterparties with master netting agreements | 0.2 | |
Designated as Hedging Instrument [Member] | Interest Rate Swap [Member] | Short-term Derivative Positions [Member] | Other Current Liabilities [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | | |
Derivative Liability, Fair Value | 0.2 | |
Derivative, Collateral, Right to Reclaim Securities | 0 | |
Derivative, Collateral, Right to Reclaim Cash | 0 | |
Liability position offset by the asset position of counterparties with master netting agreements | 0.2 | |
Not Designated as Hedging Instrument [Member] | Natural Gas Futures [Member] | Long-term Derivative Positions [Member] | Other Deferred Credit [Member] | | |
Derivative Liability, Fair Value | 0.3 | |
Derivative, Collateral, Right to Reclaim Securities | (0.2) | |
Derivative, Collateral, Right to Reclaim Cash | (0.1) | |
Liability position offset by the asset position of counterparties with master netting agreements | 0 | |
Not Designated as Hedging Instrument [Member] | Natural Gas Futures [Member] | Long-term Derivative Positions [Member] | Other Deferred Credit [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | | |
Derivative Liability, Fair Value | 0.3 | |
Derivative, Collateral, Right to Reclaim Securities | (0.2) | |
Derivative, Collateral, Right to Reclaim Cash | (0.1) | |
Liability position offset by the asset position of counterparties with master netting agreements | $ 0 | |