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Property, Plant and Equipment (Ownership Interests) (Details)
$ in Millions
3 Months Ended 12 Months Ended
Mar. 31, 2014
MW
Dec. 31, 2013
MW
Dec. 31, 2015
USD ($)
MW
Conesville [Member]      
Production Capacity (MW) | MW   129  
THE DAYTON POWER AND LIGHT COMPANY [Member] | Conesville [Member]      
Production Capacity (MW) | MW   129  
THE DAYTON POWER AND LIGHT COMPANY [Member] | East Bend Station [Member]      
Production Capacity (MW) | MW 186 186  
DP&L Share [Member] | Conesville [Member]      
Ownership (%)     16.50%
DP&L Share [Member] | Killen Station [Member]      
Ownership (%)     67.00%
DP&L Share [Member] | Miami Fort Units 7 and 8 [Member]      
Ownership (%)     36.00%
DP&L Share [Member] | Stuart Station [Member]      
Ownership (%)     35.00%
DP&L Share [Member] | Zimmer Station [Member]      
Ownership (%)     28.10%
DP&L Share [Member] | Total Jointly-owned Stations [Member]      
Production Capacity (MW) | MW     2,078
DP&L Share [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Conesville [Member]      
Ownership (%)     16.50%
Production Capacity (MW) | MW     129
DP&L Share [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Killen Station [Member]      
Ownership (%)     67.00%
Production Capacity (MW) | MW     402
DP&L Share [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Miami Fort Units 7 and 8 [Member]      
Ownership (%)     36.00%
Production Capacity (MW) | MW     368
DP&L Share [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Stuart Station [Member]      
Ownership (%)     35.00%
Production Capacity (MW) | MW     808
DP&L Share [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Zimmer Station [Member]      
Ownership (%)     28.10%
Production Capacity (MW) | MW     371
DP&L Share [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Total Jointly-owned Stations [Member]      
Production Capacity (MW) | MW     2,078
DP&L Investment [Member] | Conesville [Member]      
Gross Plant In Service     $ 26.0
Accumulated Depreciation     4.0
Construction Work in Process     1.0
DP&L Investment [Member] | Killen Station [Member]      
Gross Plant In Service     342.0
Accumulated Depreciation     29.0
Construction Work in Process     2.0
DP&L Investment [Member] | Miami Fort Units 7 and 8 [Member]      
Gross Plant In Service     219.0
Accumulated Depreciation     32.0
Construction Work in Process     6.0
DP&L Investment [Member] | Stuart Station [Member]      
Gross Plant In Service     236.0
Accumulated Depreciation     19.0
Construction Work in Process     18.0
DP&L Investment [Member] | Zimmer Station [Member]      
Gross Plant In Service     188.0
Accumulated Depreciation     44.0
Construction Work in Process     12.0
DP&L Investment [Member] | Transmission (At Varying Percentages) [Member]      
Gross Plant In Service     43.0
Accumulated Depreciation     8.0
DP&L Investment [Member] | Total Jointly-owned Stations [Member]      
Gross Plant In Service     1,054.0
Accumulated Depreciation     136.0
Construction Work in Process     39.0
DP&L Investment [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Conesville [Member]      
Gross Plant In Service     27.0
Accumulated Depreciation     8.0
Construction Work in Process     1.0
DP&L Investment [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Killen Station [Member]      
Gross Plant In Service     655.0
Accumulated Depreciation     326.0
Construction Work in Process     2.0
DP&L Investment [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Miami Fort Units 7 and 8 [Member]      
Gross Plant In Service     366.0
Accumulated Depreciation     171.0
Construction Work in Process     6.0
DP&L Investment [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Stuart Station [Member]      
Gross Plant In Service     772.0
Accumulated Depreciation     338.0
Construction Work in Process     18.0
DP&L Investment [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Zimmer Station [Member]      
Gross Plant In Service     1,104.0
Accumulated Depreciation     690.0
Construction Work in Process     12.0
DP&L Investment [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Transmission (At Varying Percentages) [Member]      
Gross Plant In Service     99.0
Accumulated Depreciation     64.0
DP&L Investment [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Total Jointly-owned Stations [Member]      
Gross Plant In Service     3,023.0
Accumulated Depreciation     1,597.0
Construction Work in Process     $ 39.0