Commitments and Contingencies - Schedule of Accrued Liabilities for Environmental Exposures (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended	3 Months Ended
Mar. 31, 2014	Mar. 31, 2014 Potomac Electric Power Co [Member]	Mar. 31, 2014 Delmarva Power & Light Co/De [Member]	Mar. 31, 2014 Transmission and Distribution [Member]	Mar. 31, 2014 Transmission and Distribution [Member] Potomac Electric Power Co [Member]	Mar. 31, 2014 Transmission and Distribution [Member] Delmarva Power & Light Co/De [Member]	Mar. 31, 2014 Legacy Generation Regulated [Member]	Mar. 31, 2014 Legacy Generation Regulated [Member] Potomac Electric Power Co [Member]	Mar. 31, 2014 Legacy Generation Regulated [Member] Delmarva Power & Light Co/De [Member]	Mar. 31, 2014 Legacy Generation Regulated [Member] Atlantic City Electric Co [Member]	Mar. 31, 2014 Legacy Generation Non-Regulated [Member]
Commitments and Contingencies [Line Items]
Beginning balance	$ 30	$ 21	$ 3	$ 19	$ 18	$ 1	$ 6	$ 3	$ 2	$ 1	$ 5
Accruals
Payments
Ending balance	30	21	3	19	18	1	6	3	2	1	5
Less amounts in Other Current Liabilities	4	2	2	3	2	1	1		1
Amounts in Other Deferred Credits	$ 26	$ 19	$ 1	$ 16	$ 16		$ 5	$ 3	$ 1	$ 1	$ 5

Accrual for environmental loss contingencies classified as other current liabilities.

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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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