Business Segments (Segment Financial Information) (Details) (USD $) In Millions, unless otherwise specified	2 Months Ended	3 Months Ended							9 Months Ended	12 Months Ended		3 Months Ended								12 Months Ended			1 Months Ended	12 Months Ended	1 Months Ended	12 Months Ended	1 Months Ended	12 Months Ended	1 Months Ended	12 Months Ended	1 Months Ended	12 Months Ended	1 Months Ended	12 Months Ended	11 Months Ended	12 Months Ended	11 Months Ended	12 Months Ended	11 Months Ended	12 Months Ended	11 Months Ended	12 Months Ended	11 Months Ended	12 Months Ended	11 Months Ended	12 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	Sep. 30, 2012	Dec. 31, 2012	Dec. 31, 2011	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]	Dec. 31, 2012 DP&L [Member]	Dec. 31, 2011 DP&L [Member]	Dec. 31, 2010 DP&L [Member]	Dec. 31, 2011 Successor [Member]	Dec. 31, 2012 Successor [Member]	Dec. 31, 2011 Successor [Member] Utility [Member]	Dec. 31, 2012 Successor [Member] Utility [Member]	Dec. 31, 2011 Successor [Member] Competitive Retail [Member]	Dec. 31, 2012 Successor [Member] Competitive Retail [Member]	Dec. 31, 2011 Successor [Member] Other Reportable Business Segment [Member]	Dec. 31, 2012 Successor [Member] Other Reportable Business Segment [Member]	Dec. 31, 2011 Successor [Member] Adjustments and Eliminations [Member]	Dec. 31, 2012 Successor [Member] Adjustments and Eliminations [Member]	Dec. 31, 2011 Successor [Member] Parent Company [Member]	Dec. 31, 2012 Successor [Member] Parent Company [Member]	Nov. 27, 2011 Predecessor [Member]	Dec. 31, 2010 Predecessor [Member]	Nov. 27, 2011 Predecessor [Member] Utility [Member]	Dec. 31, 2010 Predecessor [Member] Utility [Member]	Nov. 27, 2011 Predecessor [Member] Competitive Retail [Member]	Dec. 31, 2010 Predecessor [Member] Competitive Retail [Member]	Nov. 27, 2011 Predecessor [Member] Other Reportable Business Segment [Member]	Dec. 31, 2010 Predecessor [Member] Other Reportable Business Segment [Member]	Nov. 27, 2011 Predecessor [Member] Adjustments and Eliminations [Member]	Dec. 31, 2010 Predecessor [Member] Adjustments and Eliminations [Member]	Nov. 27, 2011 Predecessor [Member] Parent Company [Member]	Dec. 31, 2010 Predecessor [Member] Parent Company [Member]
Revenues from external customers																									$ 116.2	$ 1,138.4	$ 38.2	$ 493.1	$ 2.5	$ 36.9			$ 156.9	$ 1,668.4			$ 1,234.5	$ 1,500.3	$ 387.2	$ 277.0	$ 49.2	$ 54.1			$ 1,670.9	$ 1,831.4
Intersegment revenues																									27.8	393.4			0.3	3.4	(28.1)	(396.8)					299.2	238.5			3.7	4.5	(302.9)	(243.0)
Total revenues	259.4	497.5	433.4	480.6	458.0	502.3	434.1	437.0				378.4	452.5	397.0	449.8	430.0	472.4	412.6	423.8				156.9	1,668.4	144.0	1,531.8	38.2	493.1	2.8	40.3	(28.1)	(396.8)	156.9	1,668.4	1,670.9	1,831.4	1,533.7	1,738.8	387.2	277.0	52.9	58.6	(302.9)	(243.0)	1,670.9	1,831.4
Fuel Costs																							35.8	361.9	34.5	354.9			1.3	7.0			35.8	361.9	355.8	383.9	346.1	371.9			9.7	12.0			355.8	383.9
Purchased power																							36.7	342.1	31.0	309.5	33.4	424.5		1.5	(27.7)	(393.4)	36.7	342.1	404.6	387.4	370.6	383.5	330.5	238.5	2.7	3.9	(299.2)	(238.5)	404.6	387.4
Amortization of intangibles										(108.1)	(13.3)												11.6	95.1					11.6	95.1			11.6	95.1
Gross margin																							72.8	869.3	78.5	867.4	4.8	68.6	(10.1)	(63.3)	(0.4)	(3.4)	72.8	869.3	910.5	1,060.1	817.0	983.4	56.7	38.5	40.5	42.7	(3.7)	(4.5)	910.5	1,060.1
Depreciation and amortization																							11.6	125.4	12.7	141.3		0.4	(1.1)	(16.3)			11.6	125.4	129.4	139.4	122.2	130.7	0.6	0.2	6.6	8.5			129.4	139.4
Goodwill, Impairment Loss									1,850.0	1,817.2										(1,817.2)				1,817.2						1,817.2				1,817.2
Fixed asset impairment																				80.8						80.8				(80.8)
Interest expense																							11.5	122.9	2.8	39.1	0.1	0.6	8.8	83.9	(0.2)	(0.7)	11.5	122.9	58.7	70.6	35.4	37.1	0.2		23.4	33.5	(0.3)		58.7	70.6
Income tax expense (benefit)																				55.1	104.2	135.2	0.6	47.7	5.8	55.1	1.1	18.1	(6.3)	(25.5)			0.6	47.7	102.0	143.0	98.4	135.2	16.7	10.5	(13.1)	(2.7)			102.0	143.0
Net income (loss)	8.2	67.1	31.7	43.5	71.5	86.4	61.4	71.0				45.8	63.9	30.8	52.7	63.0	83.2	59.4	72.1				(6.2)	(1,729.8)	45.8	91.2	1.7	22.8	(53.7)	(1,725.4)		(118.4)	(6.2)	(1,729.8)	150.5	290.3	147.4	277.7	24.1	18.8	(21.0)	(3.5)		(2.7)	150.5	290.3
Total Assets										4,247.3	6,136.2														3,538.3	3,464.2	69.9	99.2	2,528.0	683.9			6,136.2	4,247.3				3,475.4		35.7		302.2				3,813.3
Capital expenditures																									$ 30.5	$ 195.5				$ 2.6			$ 30.5	$ 198.1			$ 174.0	$ 148.2			$ 0.2	$ 3.2			$ 174.2	$ 151.4