Selected Quarterly Information (Unaudited) (Details) (USD $)	2 Months Ended	3 Months Ended							11 Months Ended	12 Months Ended	3 Months Ended
	Nov. 27, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Nov. 27, 2011	Dec. 31, 2010	Dec. 31, 2012 DP&L [Member]	Sep. 30, 2012 DP&L [Member]	Jun. 30, 2012 DP&L [Member]	Mar. 31, 2012 DP&L [Member]	Dec. 31, 2010 DP&L [Member]	Sep. 30, 2010 DP&L [Member]	Jun. 30, 2010 DP&L [Member]	Mar. 31, 2010 DP&L [Member]
Revenues	$ 259,400,000	$ 497,500,000	$ 433,400,000	$ 480,600,000	$ 458,000,000	$ 502,300,000	$ 434,100,000	$ 437,000,000			$ 378,400,000	$ 452,500,000	$ 397,000,000	$ 449,800,000	$ 430,000,000	$ 472,400,000	$ 412,600,000	$ 423,800,000
Operating income	48,200,000	112,900,000	65,800,000	100,900,000	124,500,000	144,600,000	109,300,000	126,000,000			74,800,000	100,000,000	55,800,000	89,300,000	102,900,000	131,900,000	97,000,000	118,400,000
Net income	8,200,000	67,100,000	31,700,000	43,500,000	71,500,000	86,400,000	61,400,000	71,000,000			45,800,000	63,900,000	30,800,000	52,700,000	63,000,000	83,200,000	59,400,000	72,100,000
Basic	$ 0.07	$ 0.58	$ 0.28	$ 0.38	$ 0.62	$ 0.75	$ 0.53	$ 0.61	$ 1.31	$ 2.51
Diluted	$ 0.07	$ 0.58	$ 0.28	$ 0.38	$ 0.62	$ 0.74	$ 0.53	$ 0.61	$ 1.31	$ 2.50
Dividends declared and paid per share	$ 0.5400	$ 0.3325	$ 0.3325	$ 0.3325
Earnings on common stock											45,500,000	63,700,000	30,600,000	52,500,000	62,700,000	83,000,000	59,200,000	71,900,000
Dividends paid on common stock to parent					$ 0.3025	$ 0.3025	$ 0.3025	$ 0.3025			$ 40,000,000	$ 65,000,000	$ 45,000,000	$ 70,000,000	$ 150,000,000		$ 60,000,000	$ 90,000,000