Commitments and Contingencies - Schedule of Accrued Liabilities for Environmental Exposures (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2015
Commitments and Contingencies [Line Items]
Beginning balance	$ 28
Accruals	1
Payments	1
Ending balance	28
Less amounts in Other Current Liabilities	4
Amounts in Other Deferred Credits	24
Potomac Electric Power Co [Member]
Commitments and Contingencies [Line Items]
Beginning balance	19
Ending balance	19
Less amounts in Other Current Liabilities	2
Amounts in Other Deferred Credits	17
Delmarva Power & Light Co/De [Member]
Commitments and Contingencies [Line Items]
Beginning balance	3
Accruals	1
Payments	1
Ending balance	3
Less amounts in Other Current Liabilities	2
Amounts in Other Deferred Credits	1
Transmission and Distribution [Member]
Commitments and Contingencies [Line Items]
Beginning balance	17
Accruals	1
Ending balance	18
Less amounts in Other Current Liabilities	3
Amounts in Other Deferred Credits	15
Transmission and Distribution [Member] \| Potomac Electric Power Co [Member]
Commitments and Contingencies [Line Items]
Beginning balance	16
Ending balance	16
Less amounts in Other Current Liabilities	2
Amounts in Other Deferred Credits	14
Transmission and Distribution [Member] \| Delmarva Power & Light Co/De [Member]
Commitments and Contingencies [Line Items]
Beginning balance	1
Accruals	1
Ending balance	2
Less amounts in Other Current Liabilities	1
Amounts in Other Deferred Credits	1
Legacy Generation Regulated [Member]
Commitments and Contingencies [Line Items]
Beginning balance	6
Payments	1
Ending balance	5
Less amounts in Other Current Liabilities	1
Amounts in Other Deferred Credits	4
Legacy Generation Regulated [Member] \| Potomac Electric Power Co [Member]
Commitments and Contingencies [Line Items]
Beginning balance	3
Ending balance	3
Amounts in Other Deferred Credits	3
Legacy Generation Regulated [Member] \| Delmarva Power & Light Co/De [Member]
Commitments and Contingencies [Line Items]
Beginning balance	2
Payments	1
Ending balance	1
Less amounts in Other Current Liabilities	1
Legacy Generation Regulated [Member] \| Atlantic City Electric Co [Member]
Commitments and Contingencies [Line Items]
Beginning balance	1
Ending balance	1
Amounts in Other Deferred Credits	1
Legacy Generation Non-Regulated [Member]
Commitments and Contingencies [Line Items]
Beginning balance	5
Ending balance	5
Amounts in Other Deferred Credits	$ 5

Accrual for environmental loss contingencies classified as other current liabilities.

No definition available.

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- Definition

Accrual for environmental loss contingencies classified as other deferred credits.

+ References

No definition available.

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- Definition

Total costs accrued as of the balance sheet date for environmental loss contingencies.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 410

-SubTopic 30

-Section 50

-Paragraph 7

-URI http://asc.fasb.org/extlink&oid=6393242&loc=d3e13207-110859

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 450

-SubTopic 20

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14326-108349

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 450

-SubTopic 20

-Section 25

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6395460&loc=d3e13647-108346

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- Definition

The aggregate amount disbursed during the reporting period to settle environmental loss contingencies.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 450

-SubTopic 20

-Section S99

-Paragraph 1

-Subparagraph (SAB TOPIC 5.Y.Q2)

-URI http://asc.fasb.org/extlink&oid=27011672&loc=d3e149879-122751

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- Definition

The amount added to the accrual for newly incurred environmental loss contingencies. These additions include remediation expense and interest accretion. These additions do not relate to changes in the environmental accrual related to a business acquisition or divestiture, to currency movements, or revisions in previously existing estimates.

+ References

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