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Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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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.

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Income Taxes - Narrative (Details) - USD ($) $ in Millions			6 Months Ended	9 Months Ended	12 Months Ended
Income Taxes - Narrative (Details) - USD ($) $ in Millions	Jun. 05, 2019	Jul. 01, 2017	Jun. 30, 2017	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Mar. 31, 2019
Income Taxes [Line Items]
Income Tax Credits and Adjustments					$ 108
Current Federal, State and Local, Tax Expense (Benefit)					$ 97
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent					21.00%	21.00%	35.00%
Effective Income Tax Rate Reconciliation, Percent					19.40%	5.30%	(3.30%)
Like kind exchange [Member]
Income Taxes [Line Items]
Decrease in Unrecognized Tax Benefits is Reasonably Possible								$ 33
Exelon Generation Co L L C [Member]
Income Taxes [Line Items]
Income Tax Credits and Adjustments					$ 75
Current Federal, State and Local, Tax Expense (Benefit)					$ 66
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent					21.00%	21.00%	35.00%
Effective Income Tax Rate Reconciliation, Percent					26.90%	(29.50%)	(94.60%)
Commonwealth Edison Co [Member]
Income Taxes [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent					21.00%	21.00%	35.00%
Effective Income Tax Rate Reconciliation, Percent					19.20%	20.20%	42.40%
Commonwealth Edison Co [Member] \| Like kind exchange [Member]
Income Taxes [Line Items]
Decrease in Unrecognized Tax Benefits is Reasonably Possible								$ 2
PECO Energy Co [Member]
Income Taxes [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent					21.00%	21.00%	35.00%
Effective Income Tax Rate Reconciliation, Percent					11.00%	1.30%	19.30%
Atlantic City Electric Company [Member]
Income Taxes [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent					21.00%	21.00%	35.00%
Effective Income Tax Rate Reconciliation, Percent					0.00%	13.80%	25.20%
Delmarva Power & Light Company [Member]
Income Taxes [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent					21.00%	21.00%	35.00%
Effective Income Tax Rate Reconciliation, Percent					13.00%	15.50%	37.00%
Potomac Electric Power Company [Member]
Income Taxes [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent					21.00%	21.00%	35.00%
Effective Income Tax Rate Reconciliation, Percent					6.20%	5.10%	34.70%
Pepco Holdings LLC [Member]
Income Taxes [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent					21.00%	21.00%	35.00%
Effective Income Tax Rate Reconciliation, Percent					7.40%	7.80%	38.00%
Baltimore Gas and Electric Company [Member]
Income Taxes [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent					21.00%	21.00%	35.00%
Effective Income Tax Rate Reconciliation, Percent					18.00%	19.10%	41.50%
State and Local Jurisdiction [Member]
Income Taxes [Line Items]
Increase (Decrease) in Income Taxes					$ (23)	$ 50	$ 0
State and Local Jurisdiction [Member] \| Exelon Generation Co L L C [Member]
Income Taxes [Line Items]
Increase (Decrease) in Income Taxes					(9)	53	0
State and Local Jurisdiction [Member] \| Commonwealth Edison Co [Member]
Income Taxes [Line Items]
Increase (Decrease) in Income Taxes							0
State and Local Jurisdiction [Member] \| PECO Energy Co [Member]
Income Taxes [Line Items]
Increase (Decrease) in Income Taxes							0
State and Local Jurisdiction [Member] \| Atlantic City Electric Company [Member]
Income Taxes [Line Items]
Increase (Decrease) in Income Taxes							0
State and Local Jurisdiction [Member] \| Delmarva Power & Light Company [Member]
Income Taxes [Line Items]
Increase (Decrease) in Income Taxes					0	0	0
State and Local Jurisdiction [Member] \| Potomac Electric Power Company [Member]
Income Taxes [Line Items]
Increase (Decrease) in Income Taxes							0
State and Local Jurisdiction [Member] \| Pepco Holdings LLC [Member]
Income Taxes [Line Items]
Decrease in Unrecognized Tax Benefits is Reasonably Possible					14
Increase (Decrease) in Income Taxes					0	$ 3	0
State and Local Jurisdiction [Member] \| Baltimore Gas and Electric Company [Member]
Income Taxes [Line Items]
Increase (Decrease) in Income Taxes							$ 0
ILLINOIS
Income Taxes [Line Items]
Effective Income Tax Rate Reconciliation, Percent	10.49%	9.50%	7.75%	9.50%
Tax Year 2019 [Member] \| State and Local Jurisdiction [Member] \| Pepco Holdings LLC [Member]
Income Taxes [Line Items]
Decrease in Unrecognized Tax Benefits is Reasonably Possible					$ 21