Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Customer allowance for uncollectible accounts	$ 243	$ 283
Other allowance for uncollectible accounts	48	36
Accumulated depreciation and amortization	$ 23,979	$ 22,902
Common Stock, No Par Value	$ 0	$ 0
Common Stock, Shares Authorized	2,000,000,000	2,000,000,000
Common Stock, Shares, Outstanding	973,000,000	968,000,000
Treasury stock, shares held	2,000,000	2,000,000
Exelon Generation Co L L C [Member]
Customer allowance for uncollectible accounts	$ 80	$ 103
Other allowance for uncollectible accounts	0	1
Accumulated depreciation and amortization	12,017	12,206
Commonwealth Edison Co [Member]
Customer allowance for uncollectible accounts	59	61
Other allowance for uncollectible accounts	20	20
Accumulated depreciation and amortization	$ 5,168	$ 4,684
Commonwealth Edison Co [Member] | Common Stock [Member]
Common Stock, Par or Stated Value Per Share	$ 12.50	$ 12.50
Common Stock, Shares Authorized	250,000,000	250,000,000
Common Stock, Shares, Outstanding	127,000,000	127,000,000
Baltimore Gas and Electric Company [Member]
Customer allowance for uncollectible accounts	$ 12	$ 16
Other allowance for uncollectible accounts	5	4
Accumulated depreciation and amortization	$ 3,834	$ 3,633
Baltimore Gas and Electric Company [Member] | Common Stock [Member]
Common Stock, No Par Value	$ 0.00	$ 0.00
Common Stock, Shares Authorized	1,500	0
Common Stock, Shares, Outstanding	1,000
PECO Energy Co [Member]
Customer allowance for uncollectible accounts	$ 55	$ 53
Other allowance for uncollectible accounts	7	8
Accumulated depreciation and amortization	$ 3,718	$ 3,561
PECO Energy Co [Member] | Common Stock [Member]
Common Stock, No Par Value	$ 0	$ 0
Common Stock, Shares Authorized	500,000,000	500,000,000
Common Stock, Shares, Outstanding	170,000,000	170,000,000
Pepco Holdings LLC [Member]
Customer allowance for uncollectible accounts	$ 37	$ 50
Other allowance for uncollectible accounts	16	3
Accumulated depreciation and amortization	1,213	841
Potomac Electric Power Company [Member]
Customer allowance for uncollectible accounts	13	20
Other allowance for uncollectible accounts	7	1
Accumulated depreciation and amortization	$ 3,517	$ 3,354
Potomac Electric Power Company [Member] | Common Stock [Member]
Common Stock, Par or Stated Value Per Share	$ 0.01	$ 0.01
Common Stock, Shares Authorized	200,000,000	200,000,000
Common Stock, Shares, Outstanding	100	100
Delmarva Power & Light Company [Member]
Customer allowance for uncollectible accounts	$ 11	$ 12
Other allowance for uncollectible accounts	4	1
Accumulated depreciation and amortization	$ 1,425	$ 1,329
Delmarva Power & Light Company [Member] | Common Stock [Member]
Common Stock, Par or Stated Value Per Share	$ 2.25	$ 2.25
Common Stock, Shares Authorized	1,000	1,000
Common Stock, Shares, Outstanding	1,000	1,000
Atlantic City Electric Company [Member]
Customer allowance for uncollectible accounts	$ 13	$ 18
Other allowance for uncollectible accounts	5	1
Accumulated depreciation and amortization	$ 1,210	$ 1,137
Atlantic City Electric Company [Member] | Common Stock [Member]
Common Stock, Par or Stated Value Per Share	$ 3.00	$ 3.00
Common Stock, Shares Authorized	25,000,000	25,000,000
Common Stock, Shares, Outstanding	9,000,000	9,000,000