Fair Value Disclosures (Fair Value Of Financial Assets And Liabilities Measured On A Recurring Basis) (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012		Dec. 31, 2011
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	$ 133		$ 192
Derivative instruments, liabilities	96		128
Treasury Fund [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	46		114
Money Market Funds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Executive deferred compensation plan assets	14		18
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	27		28
Natural Gas [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, liabilities	38	[1],[2]	67	[3],[4]
Electricity [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	3	[1],[5]
Derivative instruments, liabilities	22	[1],[5]	32	[3],[6]
Capacity [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	8	[1]
Derivative instruments, liabilities	9	[1]	1	[3]
Fair Value, Inputs, Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	60	[7]	132	[8]
Derivative instruments, liabilities	27	[7]	50	[8]
Fair Value, Inputs, Level 1 [Member] | Treasury Fund [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	46	[7]	114	[8]
Fair Value, Inputs, Level 1 [Member] | Money Market Funds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Executive deferred compensation plan assets	14	[7]	18	[8]
Fair Value, Inputs, Level 1 [Member] | Natural Gas [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, liabilities	27	[1],[2],[7]	50	[3],[4],[8]
Fair Value, Inputs, Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	46	[7]	43	[8]
Derivative instruments, liabilities	49	[7]	61	[8]
Fair Value, Inputs, Level 2 [Member] | Life Insurance Contracts [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Executive deferred compensation plan assets	43	[7]	43	[8]
Executive deferred compensation plan liabilities	27	[7]	28	[8]
Fair Value, Inputs, Level 2 [Member] | Electricity [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	3	[1],[5],[7]
Derivative instruments, liabilities	22	[1],[5],[7]	32	[3],[6],[8]
Fair Value, Inputs, Level 2 [Member] | Capacity [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, liabilities			1	[3],[8]
Fair Value, Inputs, Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	27		17
Derivative instruments, liabilities	20		17
Fair Value, Inputs, Level 3 [Member] | Life Insurance Contracts [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Executive deferred compensation plan assets	19		17
Fair Value, Inputs, Level 3 [Member] | Natural Gas [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, liabilities	11	[1],[2]	17	[3],[4]
Fair Value, Inputs, Level 3 [Member] | Capacity [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	8	[1]
Derivative instruments, liabilities	9	[1]
Delmarva Power & Light Co/De [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	25		3
Derivative instruments, liabilities	10		17
Delmarva Power & Light Co/De [Member] | Treasury Fund [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	22
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
Delmarva Power & Light Co/De [Member] | Natural Gas [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, liabilities	10	[3],[9]	17	[3],[9]
Delmarva Power & Light Co/De [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	24	[7]	2	[8]
Derivative instruments, liabilities			2	[8]
Delmarva Power & Light Co/De [Member] | Fair Value, Inputs, Level 1 [Member] | Treasury Fund [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	22	[7]
Delmarva Power & Light Co/De [Member] | Fair Value, Inputs, Level 1 [Member] | Money Market Funds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Executive deferred compensation plan assets	2	[7]	2	[8]
Delmarva Power & Light Co/De [Member] | Fair Value, Inputs, Level 1 [Member] | Natural Gas [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, liabilities			2	[3],[8],[9]
Delmarva Power & Light Co/De [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	1		1
Derivative instruments, liabilities	10		15
Delmarva Power & Light Co/De [Member] | Fair Value, 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
Delmarva Power & Light Co/De [Member] | Fair Value, Inputs, Level 3 [Member] | Natural Gas [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, liabilities	10	[3],[9]	15	[3],[9]
Atlantic City Electric Co [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	32		114
Derivative instruments, liabilities	10		1
Atlantic City Electric Co [Member] | Treasury Fund [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	24		114
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] | Capacity [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	8	[1],[10]
Derivative instruments, liabilities	9	[1],[10]
Atlantic City Electric Co [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	24	[7]	114	[8]
Atlantic City Electric Co [Member] | Fair Value, Inputs, Level 1 [Member] | Treasury Fund [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	24	[7]	114	[8]
Atlantic City Electric Co [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, liabilities	1	[7]	1	[8]
Atlantic City Electric Co [Member] | Fair Value, Inputs, Level 2 [Member] | Life Insurance Contracts [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Executive deferred compensation plan liabilities	1	[7]	1	[8]
Atlantic City Electric Co [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	8
Derivative instruments, liabilities	9
Atlantic City Electric Co [Member] | Fair Value, Inputs, Level 3 [Member] | Capacity [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	8	[1],[10]
Derivative instruments, liabilities	9	[1],[10]
Potomac Electric Power Co [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	70		69
Derivative instruments, liabilities	9		10
Potomac Electric Power Co [Member] | Money Market Funds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Executive deferred compensation plan assets	12		12
Potomac Electric Power Co [Member] | Life Insurance Contracts [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Executive deferred compensation plan assets	58		57
Executive deferred compensation plan liabilities	9		10
Potomac Electric Power Co [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	12	[7]	12	[8]
Potomac Electric Power Co [Member] | Fair Value, Inputs, Level 1 [Member] | Money Market Funds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Executive deferred compensation plan assets	12	[7]	12	[8]
Potomac Electric Power Co [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	39	[7]	40	[8]
Derivative instruments, liabilities	9	[7]	10	[8]
Potomac Electric Power Co [Member] | Fair Value, Inputs, Level 2 [Member] | Life Insurance Contracts [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Executive deferred compensation plan assets	39	[7]	40	[8]
Executive deferred compensation plan liabilities	9	[7]	10	[8]
Potomac Electric Power Co [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	19		17
Potomac Electric Power Co [Member] | Fair Value, Inputs, Level 3 [Member] | Life Insurance Contracts [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Executive deferred compensation plan assets	$ 19		$ 17

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

[2] 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.

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

[4] 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.

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

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

[7] There were no transfers of instruments between level 1 and level 2 valuation categories during the six months ended June 30, 2012.

[8] There were no transfers of instruments between level 1 and level 2 valuation categories during the year ended December 31, 2011.

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

[10] Represents derivatives associated with ACE SOCAs.