Fair Value Disclosures (Fair Value Of Financial Assets And Liabilities Measured On Recurring Basis) (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013		Dec. 31, 2012
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	$ 200		$ 113
Derivative instruments, liabilities	44		53
Natural Gas [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	1	[1],[2]
Derivative instruments, liabilities			4	[1],[3]
Capacity [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	8	[1],[4]	8	[1],[4]
Derivative instruments, liabilities	11	[1],[4]	11	[1],[4]
Treasury Fund [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	112		27
Money Market Funds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Executive deferred compensation plan assets	17		17
Life Insurance Contracts [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Executive deferred compensation plan assets	62		60
Executive deferred compensation plan liabilities	29		28
Electricity [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets			1	[1],[5]
Derivative instruments, liabilities	4	[1],[5]	10	[1],[5]
Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	130	[6]	44	[7]
Level 1 [Member] | Natural Gas [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	1	[1],[2],[6]
Level 1 [Member] | Treasury Fund [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	112	[6]	27	[7]
Level 1 [Member] | Money Market Funds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Executive deferred compensation plan assets	17	[6]	17	[7]
Level 1 [Member] | Life Insurance Contracts [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Executive deferred compensation plan assets				[7]
Level 1 [Member] | Electricity [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets				[1],[5],[7]
Derivative instruments, liabilities				[1],[5],[7]
Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	43	[6]	43	[7]
Derivative instruments, liabilities	33	[6]	38	[7]
Significant Other Observable Inputs (Level 2) [Member] | Life Insurance Contracts [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Executive deferred compensation plan assets	43	[6]	42	[7]
Executive deferred compensation plan liabilities	29	[6]	28	[7]
Significant Other Observable Inputs (Level 2) [Member] | Electricity [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets			1	[1],[5],[7]
Derivative instruments, liabilities	4	[1],[5],[6]	10	[1],[5],[7]
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	27		26
Derivative instruments, liabilities	11		15
Significant Unobservable Inputs (Level 3) [Member] | Natural Gas [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, liabilities			4	[1],[3]
Significant Unobservable Inputs (Level 3) [Member] | Capacity [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	8	[1],[4]	8	[1],[4]
Derivative instruments, liabilities	11	[1],[4]	11	[1],[4]
Significant Unobservable Inputs (Level 3) [Member] | Life Insurance Contracts [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Executive deferred compensation plan assets	19		18
Significant Unobservable Inputs (Level 3) [Member] | Electricity [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets				[1],[5]
Derivative instruments, liabilities				[1],[5]
Potomac Electric Power Co [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	156		71
Derivative instruments, liabilities	8		9
Potomac Electric Power Co [Member] | Treasury Fund [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	85
Potomac Electric Power Co [Member] | Money Market Funds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Executive deferred compensation plan assets	14		15
Potomac Electric Power Co [Member] | Life Insurance Contracts [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Executive deferred compensation plan assets	57		56
Executive deferred compensation plan liabilities	8		9
Potomac Electric Power Co [Member] | Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	99	[8]	15	[7]
Potomac Electric Power Co [Member] | Level 1 [Member] | Treasury Fund [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	85	[8]
Potomac Electric Power Co [Member] | Level 1 [Member] | Money Market Funds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Executive deferred compensation plan assets	14	[8]	15	[7]
Potomac Electric Power Co [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	39	[8]	38	[7]
Derivative instruments, liabilities	8	[8]	9	[7]
Potomac Electric Power Co [Member] | Significant Other Observable Inputs (Level 2) [Member] | Life Insurance Contracts [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Executive deferred compensation plan assets	39	[8]	38	[7]
Executive deferred compensation plan liabilities	8	[8]	9	[7]
Potomac Electric Power Co [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	18		18
Potomac Electric Power Co [Member] | Significant Unobservable Inputs (Level 3) [Member] | Life Insurance Contracts [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Executive deferred compensation plan assets	18		18
Delmarva Power & Light Co/De [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	4		3
Derivative instruments, liabilities	1		4
Delmarva Power & Light Co/De [Member] | Natural Gas [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	1	[2],[9]
Derivative instruments, liabilities			4	[10],[3]
Delmarva Power & Light Co/De [Member] | Money Market Funds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Executive deferred compensation plan assets	2		2
Delmarva Power & Light Co/De [Member] | Life Insurance Contracts [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Executive deferred compensation plan assets	1		1
Executive deferred compensation plan liabilities	1
Delmarva Power & Light Co/De [Member] | Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	3	[6]	2	[7]
Delmarva Power & Light Co/De [Member] | Level 1 [Member] | Natural Gas [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	1	[2],[6],[9]
Delmarva Power & Light Co/De [Member] | Level 1 [Member] | Money Market Funds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Executive deferred compensation plan assets	2	[6]	2	[7]
Delmarva Power & Light Co/De [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, liabilities	1	[6]
Delmarva Power & Light Co/De [Member] | Significant Other Observable Inputs (Level 2) [Member] | Life Insurance Contracts [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Executive deferred compensation plan liabilities	1	[6]
Delmarva Power & Light Co/De [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	1		1
Derivative instruments, liabilities			4
Delmarva Power & Light Co/De [Member] | Significant Unobservable Inputs (Level 3) [Member] | Natural Gas [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, liabilities			4	[10],[3]
Delmarva Power & Light Co/De [Member] | Significant Unobservable Inputs (Level 3) [Member] | Life Insurance Contracts [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Executive deferred compensation plan assets	1		1
Atlantic City Electric Co [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	34		35
Derivative instruments, liabilities	12		12
Atlantic City Electric Co [Member] | Capacity [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	8	[1],[4]	8	[1],[4]
Derivative instruments, liabilities	11	[1],[4]	11	[1],[4]
Atlantic City Electric Co [Member] | Treasury Fund [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	26		27
Atlantic City Electric Co [Member] | Life Insurance Contracts [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Executive deferred compensation plan liabilities	1		1
Atlantic City Electric Co [Member] | Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	26	[6]	27	[7]
Atlantic City Electric Co [Member] | Level 1 [Member] | Treasury Fund [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	26	[6]	27	[7]
Atlantic City Electric Co [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, liabilities	1	[6]	1	[7]
Atlantic City Electric Co [Member] | Significant Other Observable Inputs (Level 2) [Member] | Life Insurance Contracts [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Executive deferred compensation plan liabilities	1	[6]	1	[7]
Atlantic City Electric Co [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	8		8
Derivative instruments, liabilities	11		11
Atlantic City Electric Co [Member] | Significant Unobservable Inputs (Level 3) [Member] | Capacity [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	8	[1],[4]	8	[1],[4]
Derivative instruments, liabilities	$ 11	[1],[4]	$ 11	[1],[4]

[1] The fair value of derivative assets and liabilities reflect netting by counterparty before the impact of collateral.

[2] Represents natural gas swaps purchased by DPL as part of a natural gas hedging program approved by the DPSC.

[3] Represents natural gas options purchased by DPL as part of a natural gas hedging program approved by the DPSC.

[4] Represents derivatives associated with ACE SOCAs.

[5] Represents wholesale electricity futures and swaps that are used mainly as part of Pepco Energy Services' retail electric supply business.

[6] There were no transfers of instruments between level 1 and level 2 valuation categories during the three months ended March 31, 2013.

[7] There were no transfers of instruments between level 1 and level 2 valuation categories during the year ended December 31, 2012.

[8] There were no transfers of instruments between level 1 and level 2 valuation categories during the three months end March 31, 2013.

[9] The fair values of derivative assets and liabilities reflect netting by counterparty before the impact of collateral.

[10] The fair value of derivative liabilities reflect netting by counterparty before the impact of collateral.