Variable Interest Entities Variable Interest Entities - Narrative (Details) $ in Millions		1 Months Ended				12 Months Ended
		Jul. 31, 2017 USD ($)	Nov. 30, 2015	Jun. 30, 2015	Jul. 30, 2014	Dec. 31, 2017 USD ($) VIE project		Dec. 31, 2016 USD ($) VIE		Dec. 31, 2015 USD ($)	Sep. 30, 2017	Jun. 30, 2017	Mar. 24, 2016 USD ($)	Mar. 23, 2016 USD ($)	Jun. 09, 2015 USD ($)	Jul. 18, 2014 USD ($)	Apr. 01, 2014 USD ($)
Variable Interest Entity [Line Items]
Inventory, Raw Materials and Supplies, Gross						$ 1,311		$ 1,274
Number of variable interest entities consolidated | VIE						5		9
Number of variable interest entities not consolidated by equity holders | VIE						7		8
Parental guarantee provided						$ 75
Severance Costs						14		$ 19
Guarantee obligations maximum exposure						56
Investments In Nonconsolidated Variable Interest Entities	[1]					251		248
Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Inventory, Raw Materials and Supplies, Gross						205	[2]	199	[3],[4]
2015 ESA Investco, LLC [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage				99.00%
Payment Guarantee [Member] | CENG [Member]
Variable Interest Entity [Line Items]
Guarantee obligations maximum exposure																	$ 245
Financial Guarantee [Member] | CENG [Member]
Variable Interest Entity [Line Items]
Guarantee obligations maximum exposure																	165
Equity interest member [Member] | 2015 ESA Investco, LLC [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage				90.00%
Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Inventory, Raw Materials and Supplies, Gross						937		935
Parental guarantee provided						$ 30
Ownership Percentage Of Consolidated Variable Interest Entities						62.00%
Wind project entities with noncontrolling equity interests | project						6
Noncontrolling equity interest ownership percentage held by third parties						1.00%
Number of projects with significant economic power | project						5
Ownership interests in project entities						99.00%
Severance Costs	[5]					$ 6		13
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount						$ 8
Exelon Generation Co L L C [Member] | ExGen Renewables Holdings, LLC [Member]
Variable Interest Entity [Line Items]
Proceeds from Sale of Interest in Partnership Unit		$ 400
Exelon Generation Co L L C [Member] | Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage						100.00%
Ownership Percentage Of Consolidated Variable Interest Entities						100.00%
Exelon Generation Co L L C [Member] | Equity Method Investment Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Parental guarantee provided						$ 275
Exelon Generation Co L L C [Member] | AGE Biomass project [Member]
Variable Interest Entity [Line Items]
Ownership interests in project entities											99.00%	90.00%
Exelon Generation Co L L C [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Inventory, Raw Materials and Supplies, Gross						205		199
Parental guarantee provided															$ 275
Exelon Generation Co L L C [Member] | CENG [Member]
Variable Interest Entity [Line Items]
Parental guarantee provided						$ 637
Ownership interest						50.01%
Due from Affiliates						$ 333											$ 400
Exelon Generation Co L L C [Member] | Distributed Energy Company [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage					90.00%
Equity Method Investment, Summarized Financial Information, Equity Excluding Noncontrolling Interests						227										$ 85
Exelon Generation Co L L C [Member] | Equity interest member [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage			69.00%
Exelon Generation Co L L C [Member] | Equity interest member [Member] | ExGen Renewables Holdings, LLC [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage		49.00%
Exelon Generation Co L L C [Member] | Equity interest member [Member] | Distributed Energy Company [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage					90.00%
Baltimore Gas and Electric Company [Member]
Variable Interest Entity [Line Items]
Inventory, Raw Materials and Supplies, Gross						40		38
Severance Costs	[5]					0		1
Baltimore Gas and Electric Company [Member] | RSB Bond Co LLC [Member]
Variable Interest Entity [Line Items]
Amount Remitted To Variable Interest Entities On Rate Stabilization Bonds						22		86		$ 86
Baltimore Gas and Electric Company [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Inventory, Raw Materials and Supplies, Gross								0
Pepco Holdings LLC [Member] | Successor [Member]
Variable Interest Entity [Line Items]
Inventory, Raw Materials and Supplies, Gross						151		116
Severance Costs	[5]					4		1
Pepco Holdings LLC [Member] | Variable Interest Entity, Primary Beneficiary [Member] | Successor [Member]
Variable Interest Entity [Line Items]
Inventory, Raw Materials and Supplies, Gross						0	[2]	0	[3]
Atlantic City Electric Company [Member]
Variable Interest Entity [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets													$ 1,200
Severance Costs	[5]					1		0
Guarantee obligations maximum exposure						15
Atlantic City Electric Company [Member] | ATF [Member]
Variable Interest Entity [Line Items]
Cash Remitted To VIE						48		60		$ 61
Atlantic City Electric Company [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Inventory, Raw Materials and Supplies, Gross						$ 0		$ 0
Pepco Holdings LLC [Member]
Variable Interest Entity [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets														$ 4,005

[1] These items represent amounts on the unconsolidated VIE balance sheets, not on Exelon’s or Generation’s Consolidated Balance Sheets. These items are included to provide information regarding the relative size of the unconsolidated VIEs.

[2] Includes certain purchase accounting adjustments not pushed down to the ACE standalone entity

[3] Includes certain purchase accounting adjustments not pushed down to the ACE standalone entity.

[4] Includes certain purchase accounting adjustments not pushed down to the BGE standalone entity.

[5] The amounts above for Generation, ComEd, PECO, BGE, and PHI include immaterial amounts billed by BSC for the years ended December 31, 2017 and 2016. Pepco, DPL, and ACE include immaterial amounts billed by PHISCO for the year ended December 31, 2017. Pepco, DPL, and ACE did not have any ongoing severance plans for the year ended December 31, 2016