Debt and Credit Agreements - Retirement and Redemptions of Current and Long-Term Debt (Details) - USD ($) $ in Millions				9 Months Ended
		Oct. 15, 2015	Oct. 05, 2015	Sep. 30, 2015	Sep. 30, 2014
Debt Instrument [Line Items]
Repayments of Long-term Debt				$ 1,745	$ 1,214
Senior Notes [Member] | SeniorSecuredNotes455Jun152015 [Member]
Debt Instrument [Line Items]
Interest Rate				4.55%
Repayments of Long-term Debt	[1]			$ 550
SeniorNotes490June152015 [Member] | SeniorNotes490June152015 [Member]
Debt Instrument [Line Items]
Interest Rate				4.90%
Repayments of Long-term Debt				$ 800
Notes Payable, Other Payables [Member] | SoftwareLicense395May012024 [Member]
Debt Instrument [Line Items]
Interest Rate				3.95%
Repayments of Long-term Debt				$ 1
Exelon Generation Co L L C [Member]
Debt Instrument [Line Items]
Repayments of Long-term Debt				$ 64	$ 552
Exelon Generation Co L L C [Member] | AVSR DOE Member [Member] | Minimum [Member]
Debt Instrument [Line Items]
Interest Rate					2.33%
Exelon Generation Co L L C [Member] | AVSR DOE Member [Member] | Maximum [Member]
Debt Instrument [Line Items]
Interest Rate				3.56%	3.55%
Exelon Generation Co L L C [Member] | AVSR [Member]
Debt Instrument [Line Items]
Repayments of Long-term Debt				$ 12
Exelon Generation Co L L C [Member] | AVSR [Member] | Minimum [Member]
Debt Instrument [Line Items]
Interest Rate				2.29%	3.06%
Exelon Generation Co L L C [Member] | AVSR [Member] | Maximum [Member]
Debt Instrument [Line Items]
Interest Rate				2.96%	3.14%
Exelon Generation Co L L C [Member] | AVSR [Member] | Subsequent Event [Member]
Debt Instrument [Line Items]
Repayments of Secured Debt			$ 10
Exelon Generation Co L L C [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Interest Rate					4.40%
Repayments of Long-term Debt					$ 9
Exelon Generation Co L L C [Member] | Senior Notes [Member] | SeniorSecuredNotes525January152014Member [Member]
Debt Instrument [Line Items]
Interest Rate					5.35%
Repayments of Long-term Debt					$ 500
Exelon Generation Co L L C [Member] | Senior Notes [Member] | ExgenRenewables425February62021 [Member]
Debt Instrument [Line Items]
Interest Rate					5.25%
Exelon Generation Co L L C [Member] | Senior Notes [Member] | SeniorSecuredNotes455Jun152015 [Member]
Debt Instrument [Line Items]
Interest Rate				4.55%
Repayments of Long-term Debt	[1]			$ 550
Exelon Generation Co L L C [Member] | Pollution Control Notes [Member] | Pollution Control Notes [Member]
Debt Instrument [Line Items]
Interest Rate					4.10%
Repayments of Long-term Debt					$ 20
Exelon Generation Co L L C [Member] | Capital Lease Obligations [Member] | Continental Wind 6000 February 28, 2033 [Member]
Debt Instrument [Line Items]
Interest Rate				7.83%	7.83%
Repayments of Long-term Debt				$ 3	$ 2
Exelon Generation Co L L C [Member] | Subordinated Debt [Member] | ExgenRenewables425February62021 [Member]
Debt Instrument [Line Items]
Interest Rate				5.25%	4.44%
Repayments of Long-term Debt				$ 14	$ 3
Exelon Generation Co L L C [Member] | Subordinated Debt [Member] | ExgenRenewables425February62021 [Member] | Subsequent Event [Member]
Debt Instrument [Line Items]
Interest Rate		5.25%
Repayments of Long-term Debt		$ 10
Exelon Generation Co L L C [Member] | Subordinated Debt [Member] | Clear Horizon solar [Member]
Debt Instrument [Line Items]
Interest Rate				2.56%	2.56%
Repayments of Long-term Debt				$ 1	$ 1
Exelon Generation Co L L C [Member] | Subordinated Debt [Member] | Sacramento Solar [Member]
Debt Instrument [Line Items]
Interest Rate				2.58%	2.56%
Repayments of Long-term Debt				$ 1	$ 1
Exelon Generation Co L L C [Member] | Subordinated Debt [Member] | Continental Wind 6000 February 28, 2033 [Member]
Debt Instrument [Line Items]
Interest Rate				6.00%	6.00%
Repayments of Long-term Debt				$ 20	$ 20
Exelon Generation Co L L C [Member] | Subordinated Debt [Member] | ExGen Texas Power [Member]
Debt Instrument [Line Items]
Interest Rate				4.94%
Repayments of Long-term Debt				$ 5
Exelon Generation Co L L C [Member] | Subordinated Debt [Member] | UpstreamGasLending221July222016[Member]
Debt Instrument [Line Items]
Interest Rate				2.44%
Repayments of Long-term Debt				$ 9
Exelon Generation Co L L C [Member] | Unsecured Debt [Member] | ExGen Texas Power [Member]
Debt Instrument [Line Items]
Interest Rate					4.94%
Exelon Generation Co L L C [Member] | AVSR DOE Member [Member]
Debt Instrument [Line Items]
Repayments of Long-term Debt					$ 4
Baltimore Gas and Electric Company [Member]
Debt Instrument [Line Items]
Repayments of Long-term Debt				$ 37	$ 35
Baltimore Gas and Electric Company [Member] | Rate Stabilization Bonds, April 1, 2017 [Member] | Rate Stabilization Bonds, April 1, 2017 [Member]
Debt Instrument [Line Items]
Interest Rate					5.72%
Repayments of Long-term Debt					$ 35
Baltimore Gas and Electric Company [Member] | Rate Stabilization Bonds, April 1, 2017 [Member] | RateStabilization572April12016 [Member]
Debt Instrument [Line Items]
Interest Rate				5.72%
Repayments of Long-term Debt				$ 37
Commonwealth Edison Co [Member]
Debt Instrument [Line Items]
Repayments of Long-term Debt				$ 260	$ 617
Commonwealth Edison Co [Member] | Pollution Control Notes [Member] | Pollution Control Notes [Member]
Debt Instrument [Line Items]
Interest Rate					5.85%
Repayments of Long-term Debt					$ 17
Commonwealth Edison Co [Member] | First Mortgage Bonds [Member] | FirstMortgageBond163January12014 [Member]
Debt Instrument [Line Items]
Interest Rate					1.63%
Repayments of Long-term Debt					$ 600
Commonwealth Edison Co [Member] | First Mortgage Bonds [Member] | FMBSeries470April152015 [Member]
Debt Instrument [Line Items]
Interest Rate				4.70%
Repayments of Long-term Debt				$ 260

[1] (a)As part of the 2012 Constellation merger, Exelon and subsidiaries of Generation assumed intercompany loan agreements that mirrored the terms and amounts of external obligations held by Exelon, resulting in intercompany notes payable at Generation and Exelon Corporate