Supplemental Financial Information (Supplemental Financial Information) (Details) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Supplemental Financial Information [Line Items]
Accounts receivable, net		$ 31.0
Unbilled revenue	$ 38.9	43.3
Customer receivables	54.1	56.4
Amounts due from partners in jointly owned stations	10.9	16.0
Other	4.9	6.0
Provision for uncollectible accounts	(1.0)	(0.8)
Total accounts receivable, net	107.8	120.9
Fuel and limestone	49.9	72.2
Plant materials and supplies	35.7	34.9
Other	1.9	2.0
Total inventories, at average cost	87.5	109.1
THE DAYTON POWER AND LIGHT COMPANY [Member]
Supplemental Financial Information [Line Items]
Unbilled revenue	38.9	43.3
Customer receivables	50.8	54.1
Amounts due from partners in jointly owned stations	10.9	16.0
Other	6.0	6.9
Provision for uncollectible accounts	(1.0)	(0.8)
Total accounts receivable, net	105.6	119.5
Fuel and limestone	50.0	72.2
Plant materials and supplies	34.4	33.7
Other	2.0	2.1
Total inventories, at average cost	$ 86.4	$ 108.0