Common Stock - Schedule of Stock-based Compensation Expense (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Common Stock [Abstract]
Performance share awards	$ 59exc_PerformanceSharesExpense	$ 48exc_PerformanceSharesExpense	$ 46exc_PerformanceSharesExpense
Restricted stock units	61us-gaap_RestrictedStockExpense	61us-gaap_RestrictedStockExpense	50us-gaap_RestrictedStockExpense
Stock options	2us-gaap_StockOptionPlanExpense	3us-gaap_StockOptionPlanExpense	15us-gaap_StockOptionPlanExpense
Other stock-based awards	5	6	4
Total stock-based compensation expense included in operating and maintenance expense	127	118	115
Income tax benefit	(47)	(44)	(44)
Total after-tax stock-based compensation expense	$ 80	$ 74	$ 71

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This element includes periodic expenses for Performance Shares

+ References

No definition available.

+ Details

Name:	exc_PerformanceSharesExpense
Namespace Prefix:	exc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Stock based compensation expense components.

+ References

No definition available.

+ Details

Name:	exc_ShareBasedCompensationComponentsOtherStockBasedAwards
Namespace Prefix:	exc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Stock based compensation expense components total included in operating and maintenance expense after tax.

+ References

No definition available.

+ Details

Name:	exc_ShareBasedCompensationComponentsTotalInExpenseAfterTax
Namespace Prefix:	exc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Stock based compensation expense components total included in operating and maintenance expense pre tax.

+ References

No definition available.

+ Details

Name:	exc_ShareBasedCompensationComponentsTotalInOperatingAndMaintenancePreTax
Namespace Prefix:	exc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Stock based compensation expense income tax benefit.

+ References

No definition available.

+ Details

Name:	exc_ShareBasedCompensationIncomeTaxBenefit
Namespace Prefix:	exc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The noncash expense that represents the cost of restricted stock or unit distributed to employees as compensation.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The noncash expense that accounts for the value of stock or unit options distributed to employees as compensation.

+ References

+ Details

Name:	us-gaap_StockOptionPlanExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration