Fair Value Disclosures - Fair Value of Financial Assets and Liabilities Measured on Recurring Basis (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial instruments, assets	$ 116	$ 112
Financial instruments, liabilities	30	43
Capacity [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets		8
Derivative instruments, liabilities		11
Treasury Fund [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Restricted cash and cash equivalents	34	27
Life Insurance Contracts [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Executive deferred compensation plan assets	66	60
Executive deferred compensation plan liabilities	30	28
Natural Gas [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	1
Derivative instruments, liabilities		4
Money Market Funds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Executive deferred compensation plan assets	15	17
Quoted Prices in Active Markets for Identical Instruments (Level 1) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial instruments, assets	50	44
Financial instruments, liabilities
Quoted Prices in Active Markets for Identical Instruments (Level 1) [Member] | Capacity [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets
Derivative instruments, liabilities
Quoted Prices in Active Markets for Identical Instruments (Level 1) [Member] | Treasury Fund [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Restricted cash and cash equivalents	34	27
Quoted Prices in Active Markets for Identical Instruments (Level 1) [Member] | Life Insurance Contracts [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Executive deferred compensation plan assets
Executive deferred compensation plan liabilities
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, assets	1
Derivative instruments, liabilities
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	15	17
Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial instruments, assets	47	42
Financial instruments, liabilities	30	28
Significant Other Observable Inputs (Level 2) [Member] | Capacity [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets
Derivative instruments, liabilities
Significant Other Observable Inputs (Level 2) [Member] | Treasury Fund [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Restricted cash and cash equivalents
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	47	42
Executive deferred compensation plan liabilities	30	28
Significant Other Observable Inputs (Level 2) [Member] | Natural Gas [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets
Derivative instruments, liabilities
Significant Other Observable Inputs (Level 2) [Member] | Money Market Funds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Executive deferred compensation plan assets
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial instruments, assets	19	26
Financial instruments, liabilities		15
Significant Unobservable Inputs (Level 3) [Member] | Capacity [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] | Treasury Fund [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Restricted cash and cash equivalents
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
Executive deferred compensation plan liabilities
Significant Unobservable Inputs (Level 3) [Member] | Natural Gas [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets
Derivative instruments, liabilities		4
Significant Unobservable Inputs (Level 3) [Member] | Money Market Funds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Executive deferred compensation plan assets
Potomac Electric Power Co [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial instruments, assets	77	71
Financial instruments, liabilities	7	9
Potomac Electric Power Co [Member] | Treasury Fund [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Restricted cash and cash equivalents	3
Potomac Electric Power Co [Member] | Life Insurance Contracts [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Executive deferred compensation plan assets	61	56
Executive deferred compensation plan liabilities	7	9
Potomac Electric Power Co [Member] | Money Market Funds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Executive deferred compensation plan assets	13	15
Potomac Electric Power Co [Member] | Quoted Prices in Active Markets for Identical Instruments (Level 1) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial instruments, assets	16	15
Financial instruments, liabilities
Potomac Electric Power Co [Member] | Quoted Prices in Active Markets for Identical Instruments (Level 1) [Member] | Treasury Fund [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Restricted cash and cash equivalents	3
Potomac Electric Power Co [Member] | Quoted Prices in Active Markets for Identical Instruments (Level 1) [Member] | Life Insurance Contracts [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Executive deferred compensation plan assets
Executive deferred compensation plan liabilities
Potomac Electric Power Co [Member] | 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	13	15
Potomac Electric Power Co [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial instruments, assets	43	38
Financial instruments, liabilities	7	9
Potomac Electric Power Co [Member] | Significant Other Observable Inputs (Level 2) [Member] | Treasury Fund [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Restricted cash and cash equivalents
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	43	38
Executive deferred compensation plan liabilities	7	9
Potomac Electric Power Co [Member] | Significant Other Observable Inputs (Level 2) [Member] | Money Market Funds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Executive deferred compensation plan assets
Potomac Electric Power Co [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial instruments, assets	18	18
Financial instruments, liabilities
Potomac Electric Power Co [Member] | Significant Unobservable Inputs (Level 3) [Member] | Treasury Fund [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Restricted cash and cash equivalents
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
Executive deferred compensation plan liabilities
Potomac Electric Power Co [Member] | Significant Unobservable Inputs (Level 3) [Member] | Money Market Funds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Executive deferred compensation plan assets
Delmarva Power & Light Co/De [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial instruments, assets	3	3
Financial instruments, liabilities	1	4
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] | Natural Gas [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets	1
Derivative instruments, liabilities		4
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	1	2
Delmarva Power & Light Co/De [Member] | Quoted Prices in Active Markets for Identical Instruments (Level 1) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial instruments, assets	2	2
Financial instruments, liabilities
Delmarva Power & Light Co/De [Member] | Quoted Prices in Active Markets for Identical Instruments (Level 1) [Member] | Life Insurance Contracts [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Executive deferred compensation plan assets
Executive deferred compensation plan liabilities
Delmarva Power & Light Co/De [Member] | 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, assets	1
Derivative instruments, liabilities
Delmarva Power & Light Co/De [Member] | 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	1	2
Delmarva Power & Light Co/De [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial instruments, assets
Financial instruments, liabilities	1
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 assets
Executive deferred compensation plan liabilities	1
Delmarva Power & Light Co/De [Member] | Significant Other Observable Inputs (Level 2) [Member] | Natural Gas [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets
Derivative instruments, liabilities
Delmarva Power & Light Co/De [Member] | Significant Other Observable Inputs (Level 2) [Member] | Money Market Funds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Executive deferred compensation plan assets
Delmarva Power & Light Co/De [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial instruments, assets	1	1
Financial instruments, liabilities		4
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
Executive deferred compensation plan liabilities
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, assets
Derivative instruments, liabilities		4
Delmarva Power & Light Co/De [Member] | Significant Unobservable Inputs (Level 3) [Member] | Money Market Funds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Executive deferred compensation plan assets
Atlantic City Electric Co [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial instruments, assets	24	35
Financial instruments, liabilities		12
Atlantic City Electric Co [Member] | Capacity [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets		8
Derivative instruments, liabilities		11
Atlantic City Electric Co [Member] | Treasury Fund [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Restricted cash and cash equivalents	24	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
Atlantic City Electric Co [Member] | Quoted Prices in Active Markets for Identical Instruments (Level 1) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial instruments, assets	24	27
Financial instruments, liabilities
Atlantic City Electric Co [Member] | Quoted Prices in Active Markets for Identical Instruments (Level 1) [Member] | Capacity [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets
Derivative instruments, liabilities
Atlantic City Electric Co [Member] | Quoted Prices in Active Markets for Identical Instruments (Level 1) [Member] | Treasury Fund [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Restricted cash and cash equivalents	24	27
Atlantic City Electric Co [Member] | Quoted Prices in Active Markets for Identical Instruments (Level 1) [Member] | Life Insurance Contracts [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Executive deferred compensation plan liabilities
Atlantic City Electric Co [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial instruments, assets
Financial instruments, liabilities		1
Atlantic City Electric Co [Member] | Significant Other Observable Inputs (Level 2) [Member] | Capacity [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative instruments, assets
Derivative instruments, liabilities
Atlantic City Electric Co [Member] | Significant Other Observable Inputs (Level 2) [Member] | Treasury Fund [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Restricted cash and cash equivalents
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
Atlantic City Electric Co [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial instruments, assets		8
Financial instruments, liabilities		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
Derivative instruments, liabilities		11
Atlantic City Electric Co [Member] | Significant Unobservable Inputs (Level 3) [Member] | Treasury Fund [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Restricted cash and cash equivalents
Atlantic City Electric 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 liabilities