Commitments and Contingencies Commitments and Contingencies - Settlement Agreements (Details) - USD ($) $ in Millions		9 Months Ended	12 Months Ended
		Dec. 31, 2014	Dec. 31, 2017	Dec. 31, 2016
Guarantor Obligations [Line Items]
Nontrade Receivables, Current	[1]		$ 94	$ 109
Nontrade Receivables, Noncurrent	[2]		15	15
Accounts Payable, Other, Current	[1],[3]		(11)	$ (13)
Exelon Generation Co L L C [Member]
Guarantor Obligations [Line Items]
Spent Nuclear Fuel Storage Reimbursement	[4]		1,167
Spent Nuclear Fuel Storage Reimbursement Net Co Owners	[4],[5]		$ 1,006
Exelon Generation Co L L C [Member] | Department of Energy [Member]
Guarantor Obligations [Line Items]
Spent Nuclear Fuel Storage Reimbursement		$ 53
Spent Nuclear Fuel Storage Reimbursement Net Co Owners		$ 49

[1] Recorded in Accounts receivable, other.

[2] Recorded in Deferred debits and other assets, other

[3] Non-CENG amounts owed to co-owners are recorded in Accounts receivable, other. CENG amounts owed to co-owners are recorded in Accounts payable. Represents amounts owed to the co-owners of Peach Bottom, Quad Cities, and Nine Mile Point Unit 2 generating facilities.

[4] Includes $53 and $49, respectively, for amounts received since April 1, 2014, for costs incurred under the CENG DOE Settlement Agreements prior to the consolidation of CENG.

[5] Total after considering amounts due to co-owners of certain nuclear stations and to the former owner of Oyster Creek.