Early Plant Retirements Early Plant Retirements - Pretax Expense (Details) - USD ($) $ in Millions				12 Months Ended
		Dec. 17, 2016	Jun. 16, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Other, net				$ (112)	$ 947	$ 297
Facility Closing [Member] | TMOysterCreek [Member]
Property, Plant and Equipment [Line Items]
Restructuring Reserve, Accelerated Depreciation	[1],[2]			539
Nuclear Fuel Amortization	[1]			57
Other Cost and Expense, Operating	[1],[3]			32
Accretion Expense, Including Asset Retirement Obligations	[1]			0
Other, net	[1]			0
Other Expenses	[1]			628
Facility Closing [Member] | Three Mile Island [Member]
Property, Plant and Equipment [Line Items]
Restructuring Reserve, Accelerated Depreciation	[2],[4]				250
Nuclear Fuel Amortization	[4]				12
Other Cost and Expense, Operating	[3],[4]				77
Accretion Expense, Including Asset Retirement Obligations	[4]				0
Other, net	[4]				0
Other Expenses	[4]				339
Facility Closing [Member] | Clinton and Quad Cities [Member]
Property, Plant and Equipment [Line Items]
Restructuring Reserve, Accelerated Depreciation	[2],[5]					712
Nuclear Fuel Amortization	[5]					60
Other Cost and Expense, Operating		$ (120)	$ 146			26	[3],[5],[6]
Accretion Expense, Including Asset Retirement Obligations	[5],[7]					2
Other, net	[5],[7]					(86)
Other Expenses	[5]					714
Exelon Generation Co L L C [Member]
Property, Plant and Equipment [Line Items]
Other, net				(178)	948	401
Exelon Generation Co L L C [Member] | Facility Closing [Member] | TMOysterCreek [Member]
Property, Plant and Equipment [Line Items]
Restructuring Reserve, Accelerated Depreciation	[1],[2]			539
Nuclear Fuel Amortization	[1]			57
Other Cost and Expense, Operating	[1],[3]			32
Accretion Expense, Including Asset Retirement Obligations	[1]			0
Other, net	[1]			0
Other Expenses	[1]			$ 628
Exelon Generation Co L L C [Member] | Facility Closing [Member] | Three Mile Island [Member]
Property, Plant and Equipment [Line Items]
Restructuring Reserve, Accelerated Depreciation	[2],[4]				250
Nuclear Fuel Amortization	[4]				12
Other Cost and Expense, Operating	[3],[4]				77
Accretion Expense, Including Asset Retirement Obligations	[4]				0
Other, net	[4]				0
Other Expenses	[4]				$ 339
Exelon Generation Co L L C [Member] | Facility Closing [Member] | Clinton and Quad Cities [Member]
Property, Plant and Equipment [Line Items]
Restructuring Reserve, Accelerated Depreciation	[2],[5]					712
Nuclear Fuel Amortization	[5]					60
Other Cost and Expense, Operating		$ (120)	$ 146			26	[3],[5],[6]
Accretion Expense, Including Asset Retirement Obligations	[5],[7]					2
Other, net	[5],[7]					(86)
Other Expenses	[5]					$ 714

[1] Reflects incremental accelerated depreciation for TMI and Oyster Creek. The Oyster Creek year-to-date amounts are from February 2, 2018 through September 17, 2018.

[2] Reflects incremental accelerated depreciation of plant assets, including any ARC.

[3] Primarily includes materials and supplies inventory reserve adjustments, employee related costs and CWIP impairments. Excludes the charge to Operating and maintenance expense from the ARO remeasurement due to the announced sale of Oyster Creek. See Note 5 — Mergers, Acquisitions and Dispositions for additional information.

[4] Reflects incremental charges for TMI including incremental accelerated depreciation and amortization from May 30, 2017 through December 31, 2017.

[5] Reflects incremental charges for Clinton and Quad Cities including incremental accelerated depreciation and amortization from June 2, 2016 through December 6, 2016. In December 2016, as a result of reversing its retirement decision for Clinton and Quad Cities, Exelon and Generation updated the expected economic useful life for both facilities, to 2027 for Clinton, commensurate with the end of the Illinois ZES, and to 2032 for Quad Cities, the end of its current operating license. Depreciation was therefore adjusted beginning December 7, 2016, to reflect these extended useful life estimates.

[6] In June 2016, as a result of the retirement decision for Clinton and Quad Cities, Exelon and Generation recognized one-time charges of $146 million. In December 2016, as a result of reversing its retirement decision for Clinton and Quad Cities, Exelon and Generation reversed approximately $120 million of these one-time charges initially recorded in June 2016.

[7] For Quad Cities based on the regulatory agreement with the ICC, decommissioning-related activities are offset within Exelon's and Generation's Consolidated Statements of Operations and Comprehensive Income. The offset results in an equal adjustment to the noncurrent payables to ComEd at Generation and an adjustment to the regulatory liabilities at ComEd. Likewise, ComEd has recorded an equal noncurrent affiliate receivable from Generation and corresponding regulatory liability.