Fair Value Disclosures (Fair Value Of Financial Assets And Liabilities Measured On Recurring Basis) (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012		Dec. 31, 2011
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	$ 216		$ 192
Derivative instruments, liabilities	78		128
Money Market Funds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Executive deferred compensation plan assets	19		18
Life Insurance Contracts [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Executive deferred compensation plan assets	58		60
Executive deferred compensation plan liabilities	28		28
Natural Gas [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	1	[1],[2]
Derivative instruments, liabilities	26	[1],[2]	67	[3],[4]
Electricity [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	2	[1],[5]
Derivative instruments, liabilities	15	[1],[5]	32	[3],[5]
Capacity [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	8	[1],[6]
Derivative instruments, liabilities	9	[1],[6]	1	[3]
Treasury Fund [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	128		114
Fair Value, Inputs, Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	148	[7]	132	[8]
Derivative instruments, liabilities	18	[7]	50	[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	19	[7]	18	[8]
Fair Value, Inputs, Level 1 [Member] | Natural Gas [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	1	[1],[2],[7]
Derivative instruments, liabilities	18	[1],[2],[7]	50	[3],[4],[8]
Fair Value, Inputs, Level 1 [Member] | Treasury Fund [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	128	[7]	114	[8]
Fair Value, Inputs, Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	43	[7]	43	[8]
Derivative instruments, liabilities	43	[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	41	[7]	43	[8]
Executive deferred compensation plan liabilities	28	[7]	28	[8]
Fair Value, Inputs, Level 2 [Member] | Electricity [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	2	[1],[5],[7]
Derivative instruments, liabilities	15	[1],[5],[7]	32	[3],[5],[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	25		17
Derivative instruments, liabilities	17		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	17		17
Fair Value, Inputs, Level 3 [Member] | Natural Gas [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, liabilities	8	[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],[6]
Derivative instruments, liabilities	9	[1],[6]
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	17		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	53		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	17	[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	17	[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	36	[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	36	[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	17		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	17		17
Delmarva Power & Light Co/De [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	44		3
Derivative instruments, liabilities	7		17
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, assets	1	[1],[9]
Derivative instruments, liabilities	7	[3],[9]	17	[3],[9]
Delmarva Power & Light Co/De [Member] | Treasury Fund [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	40
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	43	[7]	2	[8]
Derivative instruments, liabilities			2	[8]
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, assets	1	[1],[7],[9]
Derivative instruments, liabilities			2	[3],[8],[9]
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	40	[7]
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	7		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	7	[3],[9]	15	[3],[9]
Atlantic City Electric Co [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	36		114
Derivative instruments, liabilities	10		1
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	[10],[6]
Derivative instruments, liabilities	9	[10],[6]
Atlantic City Electric Co [Member] | Treasury Fund [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	28		114
Atlantic City Electric Co [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	28	[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	28	[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	[10],[6]
Derivative instruments, liabilities	$ 9	[10],[6]

[1] The fair values 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 derivatives associated with ACE SOCAs.

[7] There were no transfers of instruments between level 1 and level 2 valuation categories during the nine months ended September 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] The fair value of derivative assets and liabilities reflect netting by counterparty before the impact of collateral.