Supplemental Financial Information (Supplemental Financial Information) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Unbilled revenue	$ 77.8	$ 75.2
Customer receivables	102.7	98.2
Amounts due from partners in jointly owned stations	15.8	19.7
Coal sales		1.6
Other	8.2	14.6
Provision for uncollectible accounts	(1.2)	(1.1)
Total accounts receivable, net	203.3	208.2
Fuel and Limestone	42.7	67.3
Plant materials and supplies	38.2	41.0
Other	1.8	1.8
Total inventories, at average cost	82.7	110.1
DP&L [Member]
Unbilled revenue	47.2	48.1
Customer receivables	58.2	62.0
Amounts due from partners in jointly owned stations	15.8	19.7
Coal sales		1.6
Other	27.2	29.5
Provision for uncollectible accounts	(0.9)	(0.9)
Total accounts receivable, net	147.5	160.0
Fuel and Limestone	42.9	67.3
Plant materials and supplies	37.0	39.8
Other	1.8	1.8
Total inventories, at average cost	$ 81.7	$ 108.9