Variable Interest Entities - Narrative (Details) $ in Millions			3 Months Ended	9 Months Ended	12 Months Ended
		Apr. 01, 2014 USD ($)	Mar. 23, 2016 USD ($)	Dec. 31, 2016 USD ($) project VIE	Dec. 31, 2016 USD ($) project VIE MW	Dec. 31, 2015 USD ($) VIE	Dec. 31, 2014 USD ($)	Sep. 30, 2016 USD ($)	Jun. 09, 2015 USD ($)	Jul. 18, 2014 USD ($)
Variable Interest Entity [Line Items]
Note Receivable					$ 27
Variable Interest Entity, Not Primary Beneficiary, Disclosures [Abstract]
Number of variable interest entities not consolidated by equity holders | VIE				8	8
Number of variable interest entities consolidated | VIE				9	9	7
Investments In Nonconsolidated Variable Interest Entities				$ 248	$ 248	$ 11
Consolidated Variable Interest Entity [Abstract]
Parental guarantee provided				75	75
Severance Costs					19	18
Guarantee obligations maximum exposure				50	50
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount				18	18
Equity Method Investment Variable Interest Entities [Member]
Variable Interest Entity, Not Primary Beneficiary, Disclosures [Abstract]
Investments In Nonconsolidated Variable Interest Entities				248	248	$ 11
Constellation Energy Nuclear Group [Member] | Financial Guarantee [Member]
Consolidated Variable Interest Entity [Abstract]
Guarantee obligations maximum exposure		$ 165
Constellation Energy Nuclear Group [Member] | Payment Guarantee [Member]
Consolidated Variable Interest Entity [Abstract]
Guarantee obligations maximum exposure		245
Distributed Energy Company [Member]
Variable Interest Entity [Line Items]
Equity Method Investment, Summarized Financial Information, Equity Excluding Noncontrolling Interests				250	250					$ 85
Equity Method Investment Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Equity Method Investment, Summarized Financial Information, Equity Excluding Noncontrolling Interests				$ 172	$ 172
Electricite De France LLC [Member] | Constellation Energy Nuclear Group [Member] | Financial Guarantee [Member]
Consolidated Variable Interest Entity [Abstract]
Guarantee obligations maximum exposure		145
Electricite De France LLC [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Consolidated Variable Interest Entity [Abstract]
Ownership interest				49.99%	49.99%
Pepco Holdings LLC [Member]
Variable Interest Entity, Not Primary Beneficiary, Disclosures [Abstract]
Number of variable interest entities consolidated | VIE						1
Pepco Holdings LLC [Member] | Predecessor [Member]
Consolidated Variable Interest Entity [Abstract]
Severance Costs	[1]		$ 0			$ 0
Pepco Holdings LLC [Member] | Successor [Member]
Consolidated Variable Interest Entity [Abstract]
Severance Costs	[1]			$ 1
Atlantic City Electric Company [Member]
Consolidated Variable Interest Entity [Abstract]
Guarantee obligations maximum exposure								$ 13
Atlantic City Electric Company [Member] | ATF [Member]
Consolidated Variable Interest Entity [Abstract]
Cash Remitted To VIE					$ 60	61	$ 55
Exelon Generation Co L L C [Member]
Variable Interest Entity, Not Primary Beneficiary, Disclosures [Abstract]
Investments In Nonconsolidated Variable Interest Entities				18	18
Consolidated Variable Interest Entity [Abstract]
Parental guarantee provided				$ 21	$ 21
Wind project entities with noncontrolling equity interests | project				6	6
Noncontrolling equity interest ownership percentage held by third parties				1.00%	1.00%
Number of projects with significant economic power | project				5	5
Ownership interests in project entities				99.00%	99.00%
Severance Costs	[1]				$ 13	15
Exelon Generation Co L L C [Member] | Other Severance Charges [Member]
Consolidated Variable Interest Entity [Abstract]
Severance Costs					6
Severance Obligation				$ 0	0
Exelon Generation Co L L C [Member] | Constellation Energy Nuclear Group [Member]
Consolidated Variable Interest Entity [Abstract]
Due from Affiliates		400		316	$ 316
Exelon Generation Co L L C [Member] | Equity Method Investment Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
equity interest percentage sold					69.00%
Equity Method Investment, Summarized Financial Information, Equity Excluding Noncontrolling Interests				78	$ 78
Consolidated Variable Interest Entity [Abstract]
Parental guarantee provided				275	$ 275
Exelon Generation Co L L C [Member] | Solar Project Limited Liability Companies [Member]
Consolidated Variable Interest Entity [Abstract]
Business Acquisitions, Megawatts Acquired | MW					242
Debt and Capital Lease Obligations				$ 568	$ 568
Exelon Generation Co L L C [Member] | AGE Biomass project [Member]
Consolidated Variable Interest Entity [Abstract]
Ownership interests in project entities				90.00%	90.00%
Exelon Generation Co L L C [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Consolidated Variable Interest Entity [Abstract]
Parental guarantee provided		7		$ 7	$ 7				$ 275
Remeasurement gain from derecognition of equity method investment		$ 261
Exelon Generation Co L L C [Member] | Variable Interest Entity, Primary Beneficiary [Member] | Equity Method Investment Variable Interest Entities [Member]
Consolidated Variable Interest Entity [Abstract]
Parental guarantee provided				$ 637	$ 637
Exelon Generation Co L L C [Member] | CENG [Member]
Consolidated Variable Interest Entity [Abstract]
Ownership interest				50.01%	50.01%
Exelon Generation Co L L C [Member] | Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
equity interest percentage sold					71.00%
Consolidated Variable Interest Entity [Abstract]
Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage					100.00%
Ownership Percentage Of Consolidated Variable Interest Entities					100.00%
Baltimore Gas and Electric Company [Member]
Consolidated Variable Interest Entity [Abstract]
Severance Costs	[1]				$ 1	1
Baltimore Gas and Electric Company [Member] | RSB Bond Co LLC [Member]
Consolidated Variable Interest Entity [Abstract]
Remittance of payments received from customers for rate stabilization to BondCo.					$ 86	$ 86	$ 85

[1] The amounts above for Generation, ComEd, PECO, BGE and PHI include immaterial amounts billed by BSC for the years ended December 31, 2016 and 2015.