Supplemental Financial Information (Supplemental Financial Information) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Unbilled revenue	$ 68.4	$ 77.8
Customer receivables	125.2	102.7
Amounts due from partners in jointly owned stations	20.2	15.8
Other	5.2	8.2
Provision for uncollectible accounts	(1.7)	(1.2)
Total accounts receivable, net	217.3	203.3
Fuel and Limestone	50.9	42.7
Plant materials and supplies	38.1	38.2
Other	1.8	1.8
Total inventories, at average cost	90.8	82.7
DP&L [Member]
Unbilled revenue	41.0	47.2
Customer receivables	76.9	58.2
Amounts due from partners in jointly owned stations	20.2	15.8
Other	25.5	27.2
Provision for uncollectible accounts	(1.0)	(0.9)
Total accounts receivable, net	162.6	147.5
Fuel and Limestone	50.9	42.9
Plant materials and supplies	36.9	37.0
Other	1.8	1.8
Total inventories, at average cost	$ 89.6	$ 81.7