Supplemental Financial Information (Supplemental Financial Information) (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Unbilled revenue	$ 76.0	$ 77.8
Customer receivables	112.9	102.7
Amounts due from partners in jointly owned stations	6.6	15.8
Other	2.5	8.2
Provision for uncollectible accounts	(2.0)	(1.2)
Total accounts receivable, net	196.0	203.3
Fuel and Limestone	57.9	42.7
Plant materials and supplies	35.7	38.2
Other	1.8	1.8
Total inventories, at average cost	95.4	82.7
DP&L [Member]
Unbilled revenue	48.1	47.2
Customer receivables	69.6	58.2
Amounts due from partners in jointly owned stations	6.6	15.8
Other	23.7	27.2
Provision for uncollectible accounts	(0.9)	(0.9)
Total accounts receivable, net	147.1	147.5
Fuel and Limestone	57.9	42.9
Plant materials and supplies	34.6	37.0
Other	1.8	1.8
Total inventories, at average cost	$ 94.3	$ 81.7