Fair Value Measurements (Fair Value and Cost of Non-Derivative Instruments) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012
Total Master Trust Assets, Fair Value	$ 11.5	[1]	$ 10.6	[1]
Total Assets	10.3		9.1
DP&L [Member]
Total Master Trust Assets, Cost	10.3		9.1
Total Master Trust Assets, Fair Value	11.5		10.6
Debt, Cost	877.9		903.1
Debt, Fair Value	859.6		926.9
Equity Securities [Member]
Total Master Trust Assets, Cost	3.3		4.0
Total Master Trust Assets, Fair Value	4.4	[1]	5.1	[1]
Equity Securities [Member] | DP&L [Member]
Total Master Trust Assets, Cost	3.3		4.0
Total Master Trust Assets, Fair Value	4.4		5.1
Debt Securities [Member]
Total Master Trust Assets, Cost	5.4		4.6
Total Master Trust Assets, Fair Value	5.5	[1]	5.0	[1]
Debt Securities [Member] | DP&L [Member]
Total Master Trust Assets, Cost	5.4		4.6
Total Master Trust Assets, Fair Value	5.5		5.0
Hedge Funds, Multi-strategy [Member]
Total Master Trust Assets, Fair Value			0.3	[1]
Money Market Funds [Member]
Total Master Trust Assets, Cost	0.3		0.2
Total Master Trust Assets, Fair Value	0.3	[1]	0.2	[1]
Money Market Funds [Member] | DP&L [Member]
Total Master Trust Assets, Cost	0.3		0.2
Total Master Trust Assets, Fair Value	0.3		0.2
Debt [Member]
Debt, Cost	2,294.4		2,609.9
Debt, Fair Value	2,334.6		2,707.1
Hedge Funds [Member]
Total Master Trust Assets, Cost	0.9
Total Master Trust Assets, Fair Value	0.9	[1]
Hedge Funds [Member] | DP&L [Member]
Total Master Trust Assets, Cost	0.9
Total Master Trust Assets, Fair Value	0.9
Real Estate Funds [Member]
Total Master Trust Assets, Cost	0.4		0.3
Total Master Trust Assets, Fair Value	0.4	[1]	0.3
Real Estate Funds [Member] | DP&L [Member]
Total Master Trust Assets, Cost	0.4		0.3
Total Master Trust Assets, Fair Value	$ 0.4		$ 0.3

[1] (a)Includes credit valuation adjustment