Income Taxes - Narrative (Details) - USD ($) $ in Millions	3 Months Ended				6 Months Ended	9 Months Ended
	Sep. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2017	Sep. 30, 2017	Jun. 30, 2016	Dec. 31, 2009
Income Tax Additional Narrative Information [Line Items]
Unrecognized Tax Benefits	$ 738		$ 916			$ 738
Unrecognized Tax Benefits, Interest on Income Taxes Expense				$ 94
Like kind exchange [Member]
Income Tax Additional Narrative Information [Line Items]
Unrecognized Tax Benefits	50					50
Payments for Other Taxes						950
Unrecognized Tax Benefits, Period Increase (Decrease)						2
Deferred Gain on Sale of Property								$ 1,200
Decrease in Unrecognized Tax Benefits is Reasonably Possible	39					39
IRS asserted penalties for understatement of tax				106		90
Expected non-cash charge to earnings	26					26
Early termination amount			1,250
Taxes Payable, Current	335					335	$ 360
Income Taxes Receivable	60					60
Unrecognized Tax Benefits, Income Tax Penalties Accrued	1,300					1,300
Deferred Income Tax Expense (Benefit)						350
Exelon Generation Co L L C [Member]
Income Tax Additional Narrative Information [Line Items]
Unrecognized Tax Benefits	468		490			468
Commonwealth Edison Co [Member]
Income Tax Additional Narrative Information [Line Items]
Unrecognized Tax Benefits	2		(12)			2
Unrecognized Tax Benefits, Interest on Income Taxes Expense				64
Commonwealth Edison Co [Member] | Like kind exchange [Member]
Income Tax Additional Narrative Information [Line Items]
Unrecognized Tax Benefits	15					15
Payments for Other Taxes						300
Unrecognized Tax Benefits, Period Increase (Decrease)						8
Decrease in Unrecognized Tax Benefits is Reasonably Possible	2					2
IRS asserted penalties for understatement of tax				86
Expected non-cash charge to earnings	23					23
Taxes Payable, Current				$ 150
Income Taxes Receivable	369					369
Unrecognized Tax Benefits, Income Tax Penalties Accrued	300					300
Commonwealth Edison Co [Member] | Other [Member]
Income Tax Additional Narrative Information [Line Items]
Income Taxes Receivable	23					23
PECO Energy Co [Member]
Income Tax Additional Narrative Information [Line Items]
Unrecognized Tax Benefits	0		0			0
Baltimore Gas and Electric Company [Member]
Income Tax Additional Narrative Information [Line Items]
Unrecognized Tax Benefits	120		120			120
Pepco Holdings LLC [Member] | Successor [Member]
Income Tax Additional Narrative Information [Line Items]
Unrecognized Tax Benefits	120		172			120
Potomac Electric Power Company [Member]
Income Tax Additional Narrative Information [Line Items]
Unrecognized Tax Benefits	59		80			59
Delmarva Power and Light Company [Member]
Income Tax Additional Narrative Information [Line Items]
Unrecognized Tax Benefits	21		37			21
Atlantic City Electric Company [Member]
Income Tax Additional Narrative Information [Line Items]
Unrecognized Tax Benefits	8		$ 22			8
Internal Revenue Service (IRS) [Member]
Income Tax Additional Narrative Information [Line Items]
Unrecognized Tax Benefits, Decrease Resulting from Settlements with Taxing Authorities						146
Internal Revenue Service (IRS) [Member] | Exelon Generation Co L L C [Member]
Income Tax Additional Narrative Information [Line Items]
Unrecognized Tax Benefits, Decrease Resulting from Settlements with Taxing Authorities						19
Internal Revenue Service (IRS) [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Income Tax Additional Narrative Information [Line Items]
Unrecognized Tax Benefits, Decrease Resulting from Settlements with Taxing Authorities						59
Internal Revenue Service (IRS) [Member] | Potomac Electric Power Company [Member]
Income Tax Additional Narrative Information [Line Items]
Unrecognized Tax Benefits, Decrease Resulting from Settlements with Taxing Authorities						21
Internal Revenue Service (IRS) [Member] | Delmarva Power and Light Company [Member]
Income Tax Additional Narrative Information [Line Items]
Unrecognized Tax Benefits, Decrease Resulting from Settlements with Taxing Authorities						16
Internal Revenue Service (IRS) [Member] | Atlantic City Electric Company [Member]
Income Tax Additional Narrative Information [Line Items]
Unrecognized Tax Benefits, Decrease Resulting from Settlements with Taxing Authorities						22
State and Local Jurisdiction [Member]
Income Tax Additional Narrative Information [Line Items]
Deferred Tax Assets, State Taxes	272	$ 8				272
Unrecognized tax benefits that if recognized would affect the effective tax rate	0					0
Unrecognized Tax Benefits, Increase Resulting from Settlements with Taxing Authorities		20
Decrease in Unrecognized Tax Benefits is Reasonably Possible	676					676
Increase (Decrease) in Other Deferred Liability	$ 250	28
Deferred State and Local Income Tax Expense (Benefit)						20
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Percent	9.50%				7.75%
State and Local Jurisdiction [Member] | Exelon Generation Co L L C [Member]
Income Tax Additional Narrative Information [Line Items]
Unrecognized tax benefits that if recognized would affect the effective tax rate	$ 462					462
Decrease in Unrecognized Tax Benefits is Reasonably Possible	469					469
Increase (Decrease) in Other Deferred Liability	20
Deferred State and Local Income Tax Expense (Benefit)						20
State and Local Jurisdiction [Member] | Commonwealth Edison Co [Member]
Income Tax Additional Narrative Information [Line Items]
Deferred Tax Assets, State Taxes	272					272
Increase (Decrease) in Other Deferred Liability	270
State and Local Jurisdiction [Member] | Baltimore Gas and Electric Company [Member]
Income Tax Additional Narrative Information [Line Items]
Decrease in Unrecognized Tax Benefits is Reasonably Possible	120					120
State and Local Jurisdiction [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Income Tax Additional Narrative Information [Line Items]
Deferred Tax Assets, State Taxes		8
Decrease in Unrecognized Tax Benefits is Reasonably Possible	88					88
Increase (Decrease) in Other Deferred Liability		8
State and Local Jurisdiction [Member] | Potomac Electric Power Company [Member]
Income Tax Additional Narrative Information [Line Items]
Deferred Tax Assets, State Taxes		8
Decrease in Unrecognized Tax Benefits is Reasonably Possible	59					59
Increase (Decrease) in Other Deferred Liability		$ 8
State and Local Jurisdiction [Member] | Delmarva Power and Light Company [Member]
Income Tax Additional Narrative Information [Line Items]
Decrease in Unrecognized Tax Benefits is Reasonably Possible	21					21
State and Local Jurisdiction [Member] | Atlantic City Electric Company [Member]
Income Tax Additional Narrative Information [Line Items]
Decrease in Unrecognized Tax Benefits is Reasonably Possible	$ 8					$ 8