Supplemental Financial Information (Supplemental Financial Information) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Unbilled revenue	$ 65.7	$ 77.8
Customer receivables	112.9	102.7
Amounts due from partners in jointly owned stations	10.4	15.8
Other	3.0	8.2
Provision for uncollectible accounts	(1.3)	(1.2)
Total accounts receivable, net	190.7	203.3
Fuel and Limestone	48.5	42.7
Plant materials and supplies	36.2	38.2
Other	1.7	1.8
Total inventories, at average cost	86.4	82.7
DP&L [Member]
Unbilled revenue	36.0	47.2
Customer receivables	70.3	58.2
Amounts due from partners in jointly owned stations	10.4	15.8
Other	27.0	27.2
Provision for uncollectible accounts	(0.9)	(0.9)
Total accounts receivable, net	142.8	147.5
Fuel and Limestone	48.5	42.9
Plant materials and supplies	35.0	37.0
Other	1.7	1.8
Total inventories, at average cost	$ 85.2	$ 81.7