Fair Value Disclosures (Fair Value Of Financial Assets And Liabilities Measured On Recurring Basis) (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012		Dec. 31, 2011
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	$ 113		$ 192
Derivative instruments, liabilities	64		128
Potomac Electric Power Co [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	71		69
Derivative instruments, liabilities	9		10
Delmarva Power & Light Co/De [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	3		3
Derivative instruments, liabilities	4		17
Atlantic City Electric Co [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	35		114
Derivative instruments, liabilities	12		1
Electricity [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	1	[1],[2]		[1],[3]
Derivative instruments, liabilities	10	[1],[2]	32	[1],[3]
Capacity [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	8	[2],[4]
Derivative instruments, liabilities	11	[2],[4]	1
Capacity [Member] | Atlantic City Electric Co [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	8	[3],[4]
Derivative instruments, liabilities	11
Treasury Fund [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	27		114
Treasury Fund [Member] | Atlantic City Electric Co [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	27		114
Money Market Funds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Executive deferred compensation plan assets	17		18
Money Market Funds [Member] | Potomac Electric Power Co [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Executive deferred compensation plan assets	15		12
Money Market Funds [Member] | Delmarva Power & Light Co/De [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Executive deferred compensation plan assets	2		2
Life Insurance Contracts [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Executive deferred compensation plan assets	60		60
Executive deferred compensation plan liabilities	28		28
Life Insurance Contracts [Member] | Potomac Electric Power Co [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Executive deferred compensation plan assets	56		57
Executive deferred compensation plan liabilities	9		10
Life Insurance Contracts [Member] | Delmarva Power & Light Co/De [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Executive deferred compensation plan assets	1		1
Life Insurance Contracts [Member] | Atlantic City Electric Co [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Executive deferred compensation plan liabilities	1	[3],[4]	1
Natural Gas [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, liabilities	15	[2],[5]	67	[3],[6]
Natural Gas [Member] | Delmarva Power & Light Co/De [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, liabilities	4	[1],[3]	17	[1],[2]
Quoted Prices In Active Markets For Identical Instruments (Level 1) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	44	[7]	132	[8]
Derivative instruments, liabilities	11	[7]	50	[8]
Quoted Prices In Active Markets For Identical Instruments (Level 1) [Member] | Potomac Electric Power Co [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	15	[7]	12	[8]
Quoted Prices In Active Markets For Identical Instruments (Level 1) [Member] | Delmarva Power & Light Co/De [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	2	[1]	2	[7]
Derivative instruments, liabilities			2	[7]
Quoted Prices In Active Markets For Identical Instruments (Level 1) [Member] | Atlantic City Electric Co [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	27	[7]	114	[7]
Quoted Prices In Active Markets For Identical Instruments (Level 1) [Member] | Electricity [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets				[1],[3],[8]
Quoted Prices In Active Markets For Identical Instruments (Level 1) [Member] | Treasury Fund [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	27	[7]	114	[8]
Quoted Prices In Active Markets For Identical Instruments (Level 1) [Member] | Treasury Fund [Member] | Atlantic City Electric Co [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	27	[7]	114	[7]
Quoted Prices In Active Markets For Identical Instruments (Level 1) [Member] | Money Market Funds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Executive deferred compensation plan assets	17	[7]	18	[8]
Quoted Prices In Active Markets For Identical Instruments (Level 1) [Member] | Money Market Funds [Member] | Potomac Electric Power Co [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Executive deferred compensation plan assets	15	[7]	12	[8]
Quoted Prices In Active Markets For Identical Instruments (Level 1) [Member] | Money Market Funds [Member] | Delmarva Power & Light Co/De [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Executive deferred compensation plan assets	2	[1]	2	[7]
Quoted Prices In Active Markets For Identical Instruments (Level 1) [Member] | Natural Gas [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, liabilities	11	[2],[5],[7]	50	[3],[6],[8]
Quoted Prices In Active Markets For Identical Instruments (Level 1) [Member] | Natural Gas [Member] | Delmarva Power & Light Co/De [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, liabilities			2	[1],[2],[7]
Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	43	[7]	43	[8]
Derivative instruments, liabilities	38	[7]	61	[8]
Significant Other Observable Inputs (Level 2) [Member] | Potomac Electric Power Co [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	38	[7]	40	[8]
Derivative instruments, liabilities	9	[7]	10	[8]
Significant Other Observable Inputs (Level 2) [Member] | Delmarva Power & Light Co/De [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets				[7]
Derivative instruments, liabilities				[7]
Significant Other Observable Inputs (Level 2) [Member] | Atlantic City Electric Co [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, liabilities	1	[7]	1	[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],[2],[7]		[1],[3],[8]
Derivative instruments, liabilities	10	[1],[2],[7]	32	[1],[3],[8]
Significant Other Observable Inputs (Level 2) [Member] | Capacity [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, liabilities			1	[8]
Significant Other Observable Inputs (Level 2) [Member] | Money Market Funds [Member] | Delmarva Power & Light Co/De [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Executive deferred compensation plan assets				[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	42	[7]	43	[8]
Executive deferred compensation plan liabilities	28	[7]	28	[8]
Significant Other Observable Inputs (Level 2) [Member] | Life Insurance Contracts [Member] | Potomac Electric Power Co [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Executive deferred compensation plan assets	38	[7]	40	[8]
Executive deferred compensation plan liabilities	9	[7]	10	[8]
Significant Other Observable Inputs (Level 2) [Member] | Life Insurance Contracts [Member] | Delmarva Power & Light Co/De [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Executive deferred compensation plan assets				[7]
Significant Other Observable Inputs (Level 2) [Member] | Life Insurance Contracts [Member] | Atlantic City Electric Co [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Executive deferred compensation plan liabilities	1	[3],[4],[7]	1	[7]
Significant Other Observable Inputs (Level 2) [Member] | Natural Gas [Member] | Delmarva Power & Light Co/De [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, liabilities				[1],[2],[7]
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	26		17
Derivative instruments, liabilities	15		17
Significant Unobservable Inputs (Level 3) [Member] | Potomac Electric Power Co [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	18		17
Significant Unobservable Inputs (Level 3) [Member] | Delmarva Power & Light Co/De [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	1		1
Derivative instruments, liabilities	4		15
Significant Unobservable Inputs (Level 3) [Member] | Atlantic City Electric Co [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	8
Derivative instruments, liabilities	11
Significant Unobservable Inputs (Level 3) [Member] | Electricity [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets				[1],[3]
Significant Unobservable Inputs (Level 3) [Member] | Capacity [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	8	[2],[4]
Derivative instruments, liabilities	11	[2],[4]
Significant Unobservable Inputs (Level 3) [Member] | Capacity [Member] | Atlantic City Electric Co [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	8	[3],[4]
Derivative instruments, liabilities	11
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		17
Significant Unobservable Inputs (Level 3) [Member] | Life Insurance Contracts [Member] | Potomac Electric Power Co [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Executive deferred compensation plan assets	18		17
Significant Unobservable Inputs (Level 3) [Member] | Life Insurance Contracts [Member] | Delmarva Power & Light Co/De [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Executive deferred compensation plan assets	1		1
Significant Unobservable Inputs (Level 3) [Member] | Natural Gas [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, liabilities	4	[2],[5]	17	[3],[6]
Significant Unobservable Inputs (Level 3) [Member] | Natural Gas [Member] | Delmarva Power & Light Co/De [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, liabilities	$ 4	[1],[3]	$ 15	[1],[2]

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

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

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

[4] Represents derivatives associated with ACE SOCAs.

[5] Level 1 instruments represent wholesale gas futures and swaps that are used mainly as part of Pepco Energy Services' retail energy supply business and level 3 instruments represent natural gas options purchased by DPL as part of a natural gas hedging program approved by the DPSC.

[6] Level 1 instruments represent wholesale gas futures and swaps that are used mainly as part of Pepco Energy Services' retail energy supply business and level 3 instruments represent natural gas options purchased by DPL as part of a natural gas hedging program approved by the DPSC, as well as Pepco Energy Services physical basis contracts.

[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 year ended December 31, 2011.