Supplemental Financial Information (Supplemental Financial Information) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Unbilled revenue	$ 79.2	$ 77.8
Customer receivables	104.8	102.7
Amounts due from partners in jointly owned stations	14.2	15.8
Other	4.0	8.2
Provision for uncollectible accounts	(1.3)	(1.2)
Total accounts receivable, net	200.9	203.3
Fuel and Limestone	65.3	42.7
Plant materials and supplies	33.5	38.2
Other	1.4	1.8
Total inventories, at average cost	100.2	82.7
DP&L [Member]
Unbilled revenue	49.0	47.2
Customer receivables	68.7	58.2
Amounts due from partners in jointly owned stations	14.2	15.8
Other	21.7	27.2
Provision for uncollectible accounts	(0.9)	(0.9)
Total accounts receivable, net	152.7	147.5
Fuel and Limestone	65.3	42.9
Plant materials and supplies	32.3	37.0
Other	1.4	1.8
Total inventories, at average cost	$ 99.0	$ 81.7