Income Taxes - Narrative (Details) - USD ($) $ in Millions			3 Months Ended				6 Months Ended
	Jul. 06, 2017	Jul. 06, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2017	Mar. 31, 2016	Dec. 31, 2009
Income Tax Additional Narrative Information [Line Items]
Unrecognized Tax Benefits			$ 730		$ 916		$ 730
Unrecognized Tax Benefits, Increase Resulting from Settlements with Taxing Authorities							21
Subsequent Event [Member]
Income Tax Additional Narrative Information [Line Items]
Increase (Decrease) in Income Taxes		$ 70
Increase (Decrease) in Deferred Income Taxes	$ 180
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			90			$ 106
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
Other [Member]
Income Tax Additional Narrative Information [Line Items]
IRS asserted penalties for understatement of tax						94
Exelon Generation Co L L C [Member]
Income Tax Additional Narrative Information [Line Items]
Unrecognized Tax Benefits			467		490		467
Income Taxes Receivable			16				16
Exelon Generation Co L L C [Member] | Subsequent Event [Member]
Income Tax Additional Narrative Information [Line Items]
Increase (Decrease) in Income Taxes		$ 15
Increase (Decrease) in Deferred Income Taxes	15
Commonwealth Edison Co [Member]
Income Tax Additional Narrative Information [Line Items]
Unrecognized Tax Benefits			2		(12)		2
Decrease in Unrecognized Tax Benefits is Reasonably Possible			2				2
Commonwealth Edison Co [Member] | Subsequent Event [Member]
Income Tax Additional Narrative Information [Line Items]
Increase (Decrease) in Deferred Income Taxes	$ 250
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
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]
IRS asserted penalties for understatement of tax						$ 64
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			112		172		112
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			0		$ 22		0
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]
Decrease in Unrecognized Tax Benefits is Reasonably Possible			257				257
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			50				50
Decrease in Unrecognized Tax Benefits is Reasonably Possible			57				57
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]
Decrease in Unrecognized Tax Benefits is Reasonably Possible			80				80
State and Local Jurisdiction [Member] | Potomac Electric Power Company [Member]
Income Tax Additional Narrative Information [Line Items]
Decrease in Unrecognized Tax Benefits is Reasonably Possible			59				59
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