Consolidated Statements of Comprehensive Income/(Loss) (Parenthetical) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2013	Mar. 31, 2012
Income tax (expense)/benefit on unrealized gains (losses) related to available-for-sale securities	$ (0.1)	$ (0.2)
Income tax (expense)/benefit on unrealized gains (losses) related to derivative activity	(1.1)	(4.2)
Income tax (expense)/benefit on reclassification of earnings related to derivative activity	(0.1)	0.6
Income tax (expense)/benefit on reclassification of earnings related to pension and postretirement activity	(0.3)
THE DAYTON POWER AND LIGHT COMPANY [Member]
Income tax (expense)/benefit on unrealized gains (losses) related to available-for-sale securities	(0.2)	(0.2)
Income tax (expense)/benefit on unrealized gains (losses) related to derivative activity	1.4	0.8
Income tax (expense)/benefit on reclassification of earnings related to derivative activity	0.2	0.6
Income tax (expense)/benefit on prior service cost related to pension and postretirement activity	(0.5)	(3.0)
Income tax (expense)/benefit on net loss related to pension and postretirement activity		(0.3)
Income tax (expense)/benefit on reclassification of earnings related to pension and postretirement activity		$ (0.7)

Tax effect of the income statement impact of the reclassification adjustment for prior service costs recognized as a component of net period benefit cost.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 130

-Paragraph 25

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 87

-Paragraph 25

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher AICPA

-Name Accounting Research Bulletin (ARB)

-Number 51

-Paragraph 38

-Subparagraph c(3)

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 220

-SubTopic 10

-Section 45

-Paragraph 12

-URI http://asc.fasb.org/extlink&oid=20435746&loc=d3e640-108580

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 158

-Paragraph 7

-Subparagraph a

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

- Definition

Tax effect of the increase (decrease) in the value of the projected benefit obligation and the (increase) decrease in the value of the plan assets resulting from experience different from that assumed or from a change in an actuarial assumption that has not been recognized in net periodic benefit cost.

+ References+ Details

- Definition

Tax effect of the income statement impact of the reclassification adjustment of accumulated gain (loss) from derivative instruments designated and qualifying as the effective portion of cash flow hedges realized in net income. Also includes reclassification adjustments of an entity's share of an equity investee's deferred hedging gain (loss) realized in net income.

+ References+ Details

- Definition

Tax effect of the change in accumulated gain (loss) from derivative instruments designated and qualifying as the effective portion of cash flow hedges. Also includes an entity's share of an equity investee's increase (decrease) in deferred hedging gain (loss).

+ References+ Details