Early Nuclear Plant Retirements Early Nuclear Plant Retirement - Pretax Expense (Details) - USD ($) $ in Millions		3 Months Ended				9 Months Ended		12 Months Ended
		Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Other, net		$ 237		$ 120		$ 725	$ 377
Facility Closing [Member] | Three Mile Island [Member]
Restructuring and Related Cost, Accelerated Depreciation	[1]	106				141
Nuclear Fuel Amortization		6				8
Restructuring and Related Cost, Incurred Cost		$ 112				$ 149
Facility Closing [Member] | Clinton and Quad Cities [Member]
Restructuring and Related Cost, Accelerated Depreciation	[2]		$ 253	344	$ 115			$ 712
Nuclear Fuel Amortization			23	28	9			60
Other Cost and Expense, Operating	[3]		(120)	5	141			26
Accretion Expense, Including Asset Retirement Obligations	[4]		0	2	0			2
Other, net	[4]		(31)	(41)	(14)			(86)
Restructuring and Related Cost, Incurred Cost			$ 125	$ 338	$ 251			$ 714

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

[2] Reflects incremental accelerated depreciation of plant assets, including any ARC, for the period June 2, 2016, through December 6, 2016.

[3] Primarily includes materials and supplies inventory reserve adjustments, employee related costs and CWIP impairments.

[4] For Quad Cities based on the regulatory agreement with the Illinois Commerce Commission, 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.