Asset Retirement Obligations - Narrative (Details) - USD ($)		3 Months Ended			9 Months Ended	12 Months Ended
		Dec. 31, 2018	Sep. 30, 2018	Mar. 31, 2018	Sep. 30, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jun. 30, 2018
Asset Retirement Obligations [Line Items]
Asset retirement obligations, noncurrent		$ 9,679,000,000				$ 9,679,000,000	$ 10,029,000,000
Asset Retirement Obligation, Revision of Estimate						$ 20,000,000		$ 2,000,000
Percent of additional decommissioning shortfall with recourse		50.00%				50.00%
Nuclear decommissioning trust funds		$ 11,661,000,000				$ 11,661,000,000	13,272,000,000
Spent Nuclear Fuel Obligation, Noncurrent		1,171,000,000				1,171,000,000	1,147,000,000
Line of credit facility, maximum borrowing capacity	[1]	9,704,000,000				9,704,000,000
Exelon Generation Co L L C [Member]
Asset Retirement Obligations [Line Items]
Asset Retirement Obligation, Period Increase (Decrease)					$ 180,000,000			34,000,000
Recovery Stranded Costs				$ 4,000,000			24,000,000
Asset retirement obligations, noncurrent		9,450,000,000				9,450,000,000	9,844,000,000
Asset Retirement Obligation, Revision of Estimate		203,000,000	$ 84,000,000		$ 138,000,000	0		0
Shortfall of decommissioning funds with recourse		0				0	50,000,000
Nuclear decommissioning trust funds		11,661,000,000				11,661,000,000	13,272,000,000
Spent Nuclear Fuel Obligation, Noncurrent		1,171,000,000				1,171,000,000	1,147,000,000
ZionSolutions rent payable						1.00
Line of credit facility, maximum borrowing capacity		$ 200,000,000				$ 200,000,000			$ 45,000,000
Annual average accretion of the ARO						4.863%
Number of years used in present value measurement						30 years
Historical five-year annual average after-tax return on NDT funds						5.00%
Exelon Generation Co L L C [Member] | Minimum [Member]
Asset Retirement Obligations [Line Items]
Investment Interest Rate						1000.00%
Estimated annual after tax return on nuclear decommissioning funds		5.00%				5.00%
Exelon Generation Co L L C [Member] | Maximum [Member]
Asset Retirement Obligations [Line Items]
Investment Interest Rate						7000.00%
Estimated annual after tax return on nuclear decommissioning funds		6.20%				6.20%
Nuclear Plant [Member]
Asset Retirement Obligations [Line Items]
Asset Retirement Obligation, Revision of Estimate						$ 890,000,000
Nuclear Plant [Member] | Exelon Generation Co L L C [Member]
Asset Retirement Obligations [Line Items]
Asset Retirement Obligation, Period Increase (Decrease)		$ 116,000,000						$ 178,000,000
Asset Retirement Obligation, Revision of Estimate						122,000,000
Decommissioning Liability, Noncurrent		120,000,000				120,000,000
Nuclear decommissioning
Asset Retirement Obligations [Line Items]
Proceeds from Customers						144,000,000	77,000,000
Nuclear decommissioning | Exelon Generation Co L L C [Member]
Asset Retirement Obligations [Line Items]
Asset Retirement Obligation, Period Increase (Decrease)						(77,000,000)	34,000,000
Asset Retirement Obligation, Revision of Estimate			$ 772,000,000				444,000,000
Zion Station [Member]
Asset Retirement Obligations [Line Items]
Decommissioning Liability, Noncurrent		0				0
Zion Station [Member] | Exelon Generation Co L L C [Member]
Asset Retirement Obligations [Line Items]
Decommissioning Liability, Noncurrent		0				0
Assets, Total [Member]
Asset Retirement Obligations [Line Items]
Nuclear decommissioning trust funds		$ 12,695,000,000				$ 12,695,000,000	$ 13,349,000,000

[1] Excludes $135 million of credit facility agreements arranged at minority and community banks at Generation, ComEd, PECO, BGE, Pepco, DPL and ACE with aggregate commitments of $49 million, $33 million, $34 million, $5 million, $5 million, $5 million and $5 million, respectively. These facilities expire on October 11, 2019. These facilities are solely utilized to issue letters of credit. As of December 31, 2018, letters of credit issued under these facilities totaled $5 million and $2 million for Generation and BGE, respectively.