Fair Value Measurements (Fair Value and Redemption Frequency) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011
Parent Company [Member]
Total Fair Value	$ 10.6		$ 10.3
DP&L [Member]
Total Fair Value	10.6		10.3
Equity Securities [Member]
Redemption Frequency	Immediate	[1]	Immediate	[1]
Total Fair Value	5.1	[1]	4.4	[1]
Equity Securities [Member] | DP&L [Member]
Redemption Frequency	Immediate	[1]
Total Fair Value	5.1	[1]	4.4	[1]
Debt Securities [Member]
Redemption Frequency	Immediate	[2]	Immediate	[2]
Total Fair Value	5.0	[2]	5.5	[2]
Debt Securities [Member] | DP&L [Member]
Redemption Frequency	Immediate	[2]
Total Fair Value	5.0	[2]	5.5	[2]
Money Market Funds [Member]
Redemption Frequency	Immediate	[3]	Immediate	[3]
Total Fair Value	0.2	[3]	0.2	[3]
Hedge Funds, Multi-strategy [Member]
Redemption Frequency	Immediate	[4]	Immediate	[4]
Total Fair Value	0.3	[4]	0.2	[4]
Hedge Funds, Multi-strategy [Member] | DP&L [Member]
Redemption Frequency	Immediate	[4]
Total Fair Value	$ 0.3	[4]	$ 0.2	[4]

[1] (b) This category includes investments in hedge funds representing an S&P 500 index and the Morgan Stanley Capital International (MSCI) U.S. Small Cap 1750 Index. Investments in this category can be redeemed immediately at the current net asset value per unit.

[2] (c) This category includes investments in U.S. Treasury obligations and U.S. investment grade bonds. Investments in this category can be redeemed immediately at the current net asset value per unit.

[3] (a) This category includes investments in high-quality, short-term securities. Investments in this category can be redeemed immediately at the current net asset value per unit.

[4] (d) This category includes a mix of actively managed funds holding investments in stocks, bonds and short-term investments in a mix of actively managed funds. Investments in this category can be redeemed immediately at the current net asset value per unit.