Leases Lessee - Components of Lease Cost (Details) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2019 USD ($)	Sep. 30, 2019 USD ($)
Schedule of Components of Lease Cost [Line Items]
Operating Lease Costs	$ 97	$ 252
Variable Lease Costs	79	229
Short-term Lease Costs	5	16
Total Lease Costs	181	497
Sublease Income	$ 29	$ 48
Operating Lease, Weighted Average Remaining Lease Term	10 years 1 month 6 days	10 years 1 month 6 days
Operating Lease Weighted Average Discount Rate, Percent	4.50%	4.50%
Exelon Generation Co L L C [Member]
Schedule of Components of Lease Cost [Line Items]
Operating Lease Costs	$ 73	$ 180
Variable Lease Costs	74	214
Short-term Lease Costs	5	16
Total Lease Costs	152	410
Sublease Income	$ 28	$ 42
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	0	1
Short-term Lease Costs	0	0
Total Lease Costs	$ 1	$ 3
Operating Lease, Weighted Average Remaining Lease Term	4 years 8 months 12 days	4 years 8 months 12 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	$ 1
Variable Lease Costs	0	0
Short-term Lease Costs	0	0
Total Lease Costs	$ 0	$ 1
Operating Lease, Weighted Average Remaining Lease Term	4 years 3 months 18 days	4 years 3 months 18 days
Operating Lease Weighted Average Discount Rate, Percent	3.30%	3.30%
Baltimore Gas and Electric Company [Member]
Schedule of Components of Lease Cost [Line Items]
Operating Lease Costs	$ 8	$ 25
Variable Lease Costs	1	1
Short-term Lease Costs	0	0
Total Lease Costs	$ 9	$ 26
Operating Lease, Weighted Average Remaining Lease Term	5 years 7 months 6 days	5 years 7 months 6 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	$ 12	$ 35
Variable Lease Costs	1	5
Short-term Lease Costs	0	0
Total Lease Costs	13	40
Sublease Income	$ 1	$ 6
Operating Lease, Weighted Average Remaining Lease Term	9 years	9 years
Operating Lease Weighted Average Discount Rate, Percent	4.00%	4.00%
Potomac Electric Power Company [Member]
Schedule of Components of Lease Cost [Line Items]
Operating Lease Costs	$ 3	$ 9
Variable Lease Costs	0	2
Short-term Lease Costs	0	0
Total Lease Costs	$ 3	$ 11
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	3.70%	3.70%
Delmarva Power and Light Company [Member]
Schedule of Components of Lease Cost [Line Items]
Operating Lease Costs	$ 3	$ 10
Variable Lease Costs	0	2
Short-term Lease Costs	0	0
Total Lease Costs	3	12
Sublease Income	$ 1	$ 6
Operating Lease, Weighted Average Remaining Lease Term	9 years 6 months	9 years 6 months
Operating Lease Weighted Average Discount Rate, Percent	3.70%	3.70%
Atlantic City Electric Company [Member]
Schedule of Components of Lease Cost [Line Items]
Operating Lease Costs	$ 2	$ 5
Variable Lease Costs	0	1
Short-term Lease Costs	0	0
Total Lease Costs	$ 2	$ 6
Operating Lease, Weighted Average Remaining Lease Term	5 years 3 months 18 days	5 years 3 months 18 days
Operating Lease Weighted Average Discount Rate, Percent	3.30%	3.30%