Debt Obligations (Long-term Debt Maturities) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012
Due within one year	$ 0.4
Due within two years	895.3
Due within three years	0.1
Due within four years	0.1
Due within five years	450.1
Thereafter	1,252.9
Total Maturities	2,598.9
Unamortized adjustments to market value from purchase accounting	16.0
Total	2,614.9
DP&L [Member]
Due within one year	0.4
Due within two years	470.3
Due within three years	0.1
Due within four years	0.1
Due within five years	0.1
Thereafter	432.4
Total Maturities	$ 903.4