Supplemental Financial Information (Supplemental Financial Information) (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Supplemental Financial Information [Line Items]
Unbilled revenue	$ 43.3	$ 49.1
Customer receivables	56.4	70.1
Amounts due from partners in jointly owned stations	16.0	15.2
Other	6.0	3.0
Provision for uncollectible accounts	(0.8)	(0.9)
Total accounts receivable, net	120.9	136.5
Fuel and Limestone	72.2	65.3
Plant materials and supplies	34.9	33.5
Other	2.0	1.4
Total inventories, at average cost	109.1	100.2
Assets held for sale - current	62.2	67.3
THE DAYTON POWER AND LIGHT COMPANY [Member]
Supplemental Financial Information [Line Items]
Unbilled revenue	43.3	49.0
Customer receivables	54.1	68.7
Amounts due from partners in jointly owned stations	16.0	15.2
Other	6.9	20.7
Provision for uncollectible accounts	(0.8)	(0.9)
Total accounts receivable, net	119.5	152.7
Fuel and Limestone	72.2	65.3
Plant materials and supplies	33.7	32.3
Other	2.1	1.4
Total inventories, at average cost	108.0	99.0
Accounts Receivable [Member]
Supplemental Financial Information [Line Items]
Assets held for sale - current	$ 31.0	$ 64.4