Fair Value Measurements (Fair Value and Redemption Frequency) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013		Sep. 30, 2013		Dec. 31, 2012
Total Fair Value			$ 11.6		$ 10.6
DP&L [Member]
Total Fair Value			11.6		10.6
Equity Securities [Member]
Redemption Frequency	Immediate	[1]
Total Fair Value			4.4	[1]	5.1	[1]
Equity Securities [Member] | DP&L [Member]
Total Fair Value			4.4	[1]	5.1	[1]
Debt Securities [Member]
Redemption Frequency	Immediate	[2]
Total Fair Value			5.8	[2]	5.0	[2]
Debt Securities [Member] | DP&L [Member]
Total Fair Value			5.8	[2]	5.0	[2]
Money Market Funds [Member]
Redemption Frequency	Immediate	[3]
Total Fair Value			0.1	[3]	0.2	[3]
Money Market Funds [Member] | DP&L [Member]
Total Fair Value			0.1	[3]	0.2	[3]
Hedge Funds, Multi-strategy [Member]
Redemption Frequency	Immediate	[4]
Total Fair Value					0.3	[4]
Hedge Funds, Multi-strategy [Member] | DP&L [Member]
Total Fair Value					0.3	[4]
Hedge Funds, Global Opportunity [Member]
Redemption Frequency	Immediate	[5]
Total Fair Value			0.9	[5]
Hedge Funds, Global Opportunity [Member] | DP&L [Member]
Total Fair Value			0.9	[5]
Hedge Funds [Member]
Redemption Frequency	Immediate	[6]
Total Fair Value			0.4	[6]
Hedge Funds [Member] | DP&L [Member]
Total Fair Value			$ 0.4	[6]

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

[4] (d) This category includes 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 NAV per unit.

[5] (e)This category includes hedge funds investing in fixed income securities and currencies, short and long-term equity investments, and a diversified fund with investments in bonds, stocks, real estate and commodities.

[6] (f)This category includes EFT real estate funds that invest in U.S. and International properties