Early Nuclear Plant Retirements Early Nuclear Plant Retirement - Pretax Expense (Details) - USD ($) $ in Millions		3 Months Ended				6 Months Ended		12 Months Ended
		Jun. 30, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Other Cost and Expense, Operating		$ 2,971			$ 2,505	$ 5,431	$ 5,341
Other, net		$ 205			144	488	$ 258
Facility Closing [Member]
Other Expenses								$ 714
Facility Closing [Member] | Three Mile Island [Member]
Restructuring and Related Cost, Accelerated Depreciation	[1]					35
Nuclear Fuel Amortization						2
Other Expenses						$ 37
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)
Other Expenses			$ 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 construction work-in-progress (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.