Leases Components of Lease Cost (Details) $ in Millions	3 Months Ended
	Mar. 31, 2019 USD ($)
Schedule of Components of Lease Cost [Line Items]
Operating Lease Cost	$ 68
Variable Lease Cost	73
Short-term Lease Cost	9
Total Lease Cost	150	[1]
Sublease Income	$ 3
Operating Lease, Weighted Average Remaining Lease Term	10 years
Operating Lease Weighted Average Discount Rate, Percent	4.60%
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	$ 20
Exelon Generation Co L L C [Member]
Schedule of Components of Lease Cost [Line Items]
Operating Lease Cost	46
Variable Lease Cost	68
Short-term Lease Cost	8
Total Lease Cost	122	[1]
Sublease Income	$ 2
Operating Lease, Weighted Average Remaining Lease Term	10 years 8 months 12 days
Operating Lease Weighted Average Discount Rate, Percent	4.80%
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	$ 9
Commonwealth Edison Co [Member]
Schedule of Components of Lease Cost [Line Items]
Operating Lease Cost	1
Variable Lease Cost	0
Short-term Lease Cost	0
Total Lease Cost	$ 1
Operating Lease, Weighted Average Remaining Lease Term	2 years 10 months 24 days
Operating Lease Weighted Average Discount Rate, Percent	3.30%
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	$ 0
PECO Energy Co [Member]
Schedule of Components of Lease Cost [Line Items]
Operating Lease Cost	0
Variable Lease Cost	0
Short-term Lease Cost	0
Total Lease Cost	$ 0
Operating Lease, Weighted Average Remaining Lease Term	4 years 4 months 24 days
Operating Lease Weighted Average Discount Rate, Percent	3.40%
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	$ 0
Baltimore Gas and Electric Company [Member]
Schedule of Components of Lease Cost [Line Items]
Operating Lease Cost	8
Variable Lease Cost	0
Short-term Lease Cost	0
Total Lease Cost	$ 8
Operating Lease, Weighted Average Remaining Lease Term	5 years 7 months 6 days
Operating Lease Weighted Average Discount Rate, Percent	3.60%
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	$ 0
Pepco Holdings LLC [Member]
Schedule of Components of Lease Cost [Line Items]
Operating Lease Cost	10
Variable Lease Cost	2
Short-term Lease Cost	0
Total Lease Cost	12	[1]
Sublease Income	$ 1
Operating Lease, Weighted Average Remaining Lease Term	9 years 4 months 24 days
Operating Lease Weighted Average Discount Rate, Percent	4.10%
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	$ 11
Potomac Electric Power Company [Member]
Schedule of Components of Lease Cost [Line Items]
Operating Lease Cost	3
Variable Lease Cost	0
Short-term Lease Cost	0
Total Lease Cost	$ 3
Operating Lease, Weighted Average Remaining Lease Term	9 years 10 months 24 days
Operating Lease Weighted Average Discount Rate, Percent	3.90%
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	$ 4
Delmarva Power and Light Company [Member]
Schedule of Components of Lease Cost [Line Items]
Operating Lease Cost	3
Variable Lease Cost	1
Short-term Lease Cost	0
Total Lease Cost	4	[1]
Sublease Income	$ 1
Operating Lease, Weighted Average Remaining Lease Term	9 years 9 months 18 days
Operating Lease Weighted Average Discount Rate, Percent	3.90%
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	$ 4
Atlantic City Electric Company [Member]
Schedule of Components of Lease Cost [Line Items]
Operating Lease Cost	1
Variable Lease Cost	0
Short-term Lease Cost	0
Total Lease Cost	$ 1
Operating Lease, Weighted Average Remaining Lease Term	5 years 3 months 18 days
Operating Lease Weighted Average Discount Rate, Percent	3.50%
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	$ 3

[1] Excludes $3 million, $2 million, $1 million and $1 million of sublease income recorded at Exelon, Generation, PHI and DPL.