Income Taxes - Narrative (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended
	Sep. 30, 2014	Mar. 31, 2016	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2009
Income Tax Additional Narrative Information [Line Items]
Unrecognized tax benefits that if recognized would affect the effective tax rate		$ 75
Unrecognized Tax Benefits		328
Increase (Decrease) in Income Taxes		270
Deferred tax gain under involuntary conversion provisions of the IRC						$ 1,200
IRS asserted penalties for understatement of tax		90
Expected non-cash charge to earnings				$ 265
Potential tax and interest from a successful IRS challenge of the like-kind exchange transaction position		460
Early termination amount			$ 335
Taxes Payable, Current			360
Tax Adjustments, Settlements, and Unusual Provisions		300
Fresh-Start Adjustment, Increase (Decrease), Deferred Income Tax Liabilities, Noncurrent		59
Parent Company [Member]
Income Tax Additional Narrative Information [Line Items]
Unrecognized tax benefits that if recognized would affect the effective tax rate		950			$ 1,101
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 that if recognized would affect the effective tax rate		531			534
Increase (Decrease) in Income Taxes	$ 67
Effective Income Tax Rate Reconciliation, Tax Settlement, Amount		120
Tax Adjustments, Settlements, and Unusual Provisions		6
Commonwealth Edison Co [Member]
Income Tax Additional Narrative Information [Line Items]
Unrecognized tax benefits that if recognized would affect the effective tax rate		(12)			142
Unrecognized Tax Benefits		154
Expected non-cash charge to earnings				172
Non-cash equity contributions				$ 172
Potential tax and interest from a successful IRS challenge of the like-kind exchange transaction position		275
Taxes Payable, Current			$ 65
Tax Adjustments, Settlements, and Unusual Provisions		12
PECO Energy Co [Member]
Income Tax Additional Narrative Information [Line Items]
Unrecognized tax benefits that if recognized would affect the effective tax rate		0			0
Baltimore Gas and Electric Company [Member]
Income Tax Additional Narrative Information [Line Items]
Unrecognized tax benefits that if recognized would affect the effective tax rate		120			120
Pepco Holdings, LLC [Member]
Income Tax Additional Narrative Information [Line Items]
Unrecognized tax benefits that if recognized would affect the effective tax rate		168			22
PEPCO Holdings Inc [Member]
Income Tax Additional Narrative Information [Line Items]
Unrecognized Tax Benefits, Increase Resulting from Settlements with Taxing Authorities		146
Fresh-Start Adjustment, Increase (Decrease), Deferred Income Tax Liabilities, Noncurrent		8
Potomac Electric Power Company [Member]
Income Tax Additional Narrative Information [Line Items]
Unrecognized tax benefits that if recognized would affect the effective tax rate		86			8
Unrecognized Tax Benefits, Increase Resulting from Settlements with Taxing Authorities		78
Increase (Decrease) in Income Taxes	63
Delmarva Power and Light Company [Member]
Income Tax Additional Narrative Information [Line Items]
Unrecognized tax benefits that if recognized would affect the effective tax rate		39			3
Unrecognized Tax Benefits, Increase Resulting from Settlements with Taxing Authorities		36
Increase (Decrease) in Income Taxes	$ 20
Atlantic City Electric Company [Member]
Income Tax Additional Narrative Information [Line Items]
Unrecognized tax benefits that if recognized would affect the effective tax rate		24			$ 0
Unrecognized Tax Benefits, Increase Resulting from Settlements with Taxing Authorities		$ 24