Income Taxes - Narrative (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Mar. 31, 2014	Sep. 30, 2016	Dec. 31, 2015	Mar. 31, 2013	Dec. 31, 2009
Income Tax Additional Narrative Information [Line Items]
Unrecognized Tax Benefits	$ 937			$ 937	$ 1,101
Payments for Other Taxes				1,000
Unrecognized Tax Benefits, Period Increase (Decrease)	328			164
Deferred Gain on Sale of Property							$ 1,200
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit	251			251
IRS asserted penalties for understatement of tax	90
Expected non-cash charge to earnings						$ 265
Early termination amount		$ 200
Taxes Payable, Current		150
Income Taxes Receivable	80			80
Unrecognized Tax Benefits, Income Tax Penalties Accrued	1,400			1,400
Tax Adjustments, Settlements, and Unusual Provisions				300
Parent Company [Member]
Income Tax Additional Narrative Information [Line Items]
Unrecognized Tax Benefits, Increase Resulting from Settlements with Taxing Authorities				1
Exelon Generation Co L L C [Member]
Income Tax Additional Narrative Information [Line Items]
Unrecognized Tax Benefits	516			516	534
Unrecognized tax benefits that if recognized would affect the effective tax rate	52			52
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit	52			52
Tax Adjustments, Settlements, and Unusual Provisions				6
Commonwealth Edison Co [Member]
Income Tax Additional Narrative Information [Line Items]
Unrecognized Tax Benefits	(12)			(12)	142
Unrecognized Tax Benefits, Period Increase (Decrease)	154
Expected non-cash charge to earnings			$ 172
Non-cash equity contributions			$ 172
Taxes Payable, Current		$ 150
Income Taxes Receivable	345			345
Unrecognized Tax Benefits, Income Tax Penalties Accrued	300			300
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
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit	120			120
Pepco Holdings LLC [Member]
Income Tax Additional Narrative Information [Line Items]
Unrecognized Tax Benefits	157			157
Unrecognized Tax Benefits, Period Increase (Decrease)	135
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit	79			79
Pepco Holdings LLC [Member] | Predecessor [Member]
Income Tax Additional Narrative Information [Line Items]
Unrecognized Tax Benefits					22
PEPCO Holdings Inc [Member]
Income Tax Additional Narrative Information [Line Items]
Fresh-Start Adjustment, Increase (Decrease), Deferred Income Tax Liabilities, Noncurrent	8			8
Potomac Electric Power Company [Member]
Income Tax Additional Narrative Information [Line Items]
Unrecognized Tax Benefits	79			79	8
Unrecognized Tax Benefits, Period Increase (Decrease)	71
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit	59			59
Delmarva Power and Light Company [Member]
Income Tax Additional Narrative Information [Line Items]
Unrecognized Tax Benefits	34			34	3
Unrecognized Tax Benefits, Period Increase (Decrease)	31
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit	20			20
Atlantic City Electric Company [Member]
Income Tax Additional Narrative Information [Line Items]
Unrecognized Tax Benefits	22			$ 22	$ 0
Unrecognized Tax Benefits, Period Increase (Decrease)	$ 22