Income Taxes - Long-Term Marginal State Income Tax Rate (Details) - State and Local Jurisdiction [Member] - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Long-Term Marginal State Income Tax Rate [Line Items]
Increase (Decrease) in Deferred Income Taxes	$ 23	$ (50)	$ 0
Increase (Decrease) in Income Taxes	23	(50)	0
Exelon Generation Co L L C [Member]
Long-Term Marginal State Income Tax Rate [Line Items]
Increase (Decrease) in Deferred Income Taxes	9	(53)	0
Increase (Decrease) in Income Taxes	9	(53)	0
Commonwealth Edison Co [Member]
Long-Term Marginal State Income Tax Rate [Line Items]
Increase (Decrease) in Deferred Income Taxes			0
Increase (Decrease) in Income Taxes			0
PECO Energy Co [Member]
Long-Term Marginal State Income Tax Rate [Line Items]
Increase (Decrease) in Deferred Income Taxes			0
Increase (Decrease) in Income Taxes			0
Baltimore Gas and Electric Company [Member]
Long-Term Marginal State Income Tax Rate [Line Items]
Increase (Decrease) in Deferred Income Taxes			0
Increase (Decrease) in Income Taxes			0
Pepco Holdings LLC [Member]
Long-Term Marginal State Income Tax Rate [Line Items]
Increase (Decrease) in Deferred Income Taxes	0	(4)	0
Increase (Decrease) in Income Taxes	0	(3)	0
Potomac Electric Power Company [Member]
Long-Term Marginal State Income Tax Rate [Line Items]
Increase (Decrease) in Deferred Income Taxes			0
Increase (Decrease) in Income Taxes			0
Delmarva Power & Light Company [Member]
Long-Term Marginal State Income Tax Rate [Line Items]
Increase (Decrease) in Deferred Income Taxes	0	(2)	0
Increase (Decrease) in Income Taxes	$ 0	$ 0	0
Atlantic City Electric Company [Member]
Long-Term Marginal State Income Tax Rate [Line Items]
Increase (Decrease) in Deferred Income Taxes			0
Increase (Decrease) in Income Taxes			$ 0

[Line Items] for Long-Term Marginal State Income Tax Rate [Table]

No definition available.

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- Definition

The increase (decrease) during the reporting period in the account that represents the temporary difference that results from Income or Loss that is recognized for accounting purposes but not for tax purposes and vice versa.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3602-108585

+ Details

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- Definition

The increase (decrease) during the reporting period in the amounts payable to taxing authorities for taxes that are based on the reporting entity's earnings, net of amounts receivable from taxing authorities for refunds of overpayments or recoveries of income taxes, and in deferred and other tax liabilities and assets.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3602-108585

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