Leases Components of Lease Cost (Details) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)
Schedule of Components of Lease Cost [Line Items]
Operating Lease Costs	$ 87	$ 155
Variable Lease Costs	77	150
Short-term Lease Costs	3	11
Total Lease Costs	167	316
Sublease Income	$ 16	$ 19
Operating Lease, Weighted Average Remaining Lease Term	9 years 10 months 24 days	9 years 10 months 24 days
Operating Lease Weighted Average Discount Rate, Percent	4.60%	4.60%
Exelon Generation Co L L C [Member]
Schedule of Components of Lease Cost [Line Items]
Operating Lease Costs	$ 61	$ 107
Variable Lease Costs	72	140
Short-term Lease Costs	3	11
Total Lease Costs	136	258
Sublease Income	$ 12	$ 14
Operating Lease, Weighted Average Remaining Lease Term	10 years 7 months 6 days	10 years 7 months 6 days
Operating Lease Weighted Average Discount Rate, Percent	4.80%	4.80%
Commonwealth Edison Co [Member]
Schedule of Components of Lease Cost [Line Items]
Operating Lease Costs	$ 1	$ 2
Variable Lease Costs	1	1
Short-term Lease Costs	0	0
Total Lease Costs	$ 2	$ 3
Operating Lease, Weighted Average Remaining Lease Term	4 years 10 months 24 days	4 years 10 months 24 days
Operating Lease Weighted Average Discount Rate, Percent	3.10%	3.10%
PECO Energy Co [Member]
Schedule of Components of Lease Cost [Line Items]
Operating Lease Costs	$ 0	$ 0
Variable Lease Costs	0	0
Short-term Lease Costs	0	0
Total Lease Costs	$ 0	$ 0
Operating Lease, Weighted Average Remaining Lease Term	4 years 4 months 24 days	4 years 4 months 24 days
Operating Lease Weighted Average Discount Rate, Percent	3.40%	3.40%
Baltimore Gas and Electric Company [Member]
Schedule of Components of Lease Cost [Line Items]
Operating Lease Costs	$ 9	$ 17
Variable Lease Costs	1	1
Short-term Lease Costs	0	0
Total Lease Costs	$ 10	$ 18
Operating Lease, Weighted Average Remaining Lease Term	5 years 4 months 24 days	5 years 4 months 24 days
Operating Lease Weighted Average Discount Rate, Percent	3.60%	3.60%
Pepco Holdings LLC [Member]
Schedule of Components of Lease Cost [Line Items]
Operating Lease Costs	$ 13	$ 23
Variable Lease Costs	2	4
Short-term Lease Costs	0	0
Total Lease Costs	15	27
Sublease Income	$ 4	$ 5
Operating Lease, Weighted Average Remaining Lease Term	9 years 2 months 12 days	9 years 2 months 12 days
Operating Lease Weighted Average Discount Rate, Percent	4.10%	4.10%
Potomac Electric Power Company [Member]
Schedule of Components of Lease Cost [Line Items]
Operating Lease Costs	$ 3	$ 6
Variable Lease Costs	1	1
Short-term Lease Costs	0	0
Total Lease Costs	$ 4	$ 7
Operating Lease, Weighted Average Remaining Lease Term	9 years 8 months 12 days	9 years 8 months 12 days
Operating Lease Weighted Average Discount Rate, Percent	3.80%	3.80%
Delmarva Power and Light Company [Member]
Schedule of Components of Lease Cost [Line Items]
Operating Lease Costs	$ 4	$ 7
Variable Lease Costs	0	1
Short-term Lease Costs	0	0
Total Lease Costs	4	8
Sublease Income	$ 4	$ 5
Operating Lease, Weighted Average Remaining Lease Term	9 years 7 months 6 days	9 years 7 months 6 days
Operating Lease Weighted Average Discount Rate, Percent	3.90%	3.90%
Atlantic City Electric Company [Member]
Schedule of Components of Lease Cost [Line Items]
Operating Lease Costs	$ 3	$ 4
Variable Lease Costs	1	1
Short-term Lease Costs	0	0
Total Lease Costs	$ 4	$ 5
Operating Lease, Weighted Average Remaining Lease Term	5 years 2 months 12 days	5 years 2 months 12 days
Operating Lease Weighted Average Discount Rate, Percent	3.50%	3.50%