Income Taxes - Components of Income Tax Expense (Benefit) from Continuing Operations (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Taxes [Line Items]
Income taxes	$ 373	$ 774	$ 118
Exelon Generation Co L L C [Member]
Income Taxes [Line Items]
Income taxes	249	516	(108)
Commonwealth Edison Co [Member]
Income Taxes [Line Items]
Income taxes	177	163	168
PECO Energy Co [Member]
Income Taxes [Line Items]
Income taxes	(30)	65	6
Baltimore Gas and Electric Company [Member]
Income Taxes [Line Items]
Income taxes	41	79	74
Pepco Holdings LLC [Member]
Income Taxes [Line Items]
Income taxes	(77)	38	33
Potomac Electric Power Company [Member]
Income Taxes [Line Items]
Income taxes	(7)	16	11
Delmarva Power & Light Company [Member]
Income Taxes [Line Items]
Income taxes	(25)	22	22
Atlantic City Electric Company [Member]
Income Taxes [Line Items]
Income taxes	(41)	0	12
Internal Revenue Service (IRS) [Member]
Income Taxes [Line Items]
Current	26	85	226
Deferred	156	489	(99)
Investment Tax Credit	(28)	(72)	(24)
Income taxes	67
Internal Revenue Service (IRS) [Member] | Exelon Generation Co L L C [Member]
Income Taxes [Line Items]
Current	130	147	337
Deferred	150	346	(347)
Investment Tax Credit	(25)	(69)	(21)
Income taxes	67
Internal Revenue Service (IRS) [Member] | Commonwealth Edison Co [Member]
Income Taxes [Line Items]
Current	(24)	59	(63)
Deferred	112	15	145
Investment Tax Credit	(2)	(2)	(2)
Internal Revenue Service (IRS) [Member] | PECO Energy Co [Member]
Income Taxes [Line Items]
Current	(7)	45	11
Deferred	1	20	10
Investment Tax Credit	0	0	0
Internal Revenue Service (IRS) [Member] | Baltimore Gas and Electric Company [Member]
Income Taxes [Line Items]
Current	4	(51)	(5)
Deferred	10	95	47
Investment Tax Credit	0	0	0
Internal Revenue Service (IRS) [Member] | Pepco Holdings LLC [Member]
Income Taxes [Line Items]
Current	25	43	(4)
Deferred	(129)	(34)	23
Investment Tax Credit	(1)	(1)	(1)
Internal Revenue Service (IRS) [Member] | Potomac Electric Power Company [Member]
Income Taxes [Line Items]
Current	40	16	28
Deferred	(62)	(6)	(22)
Investment Tax Credit	0	0	0
Internal Revenue Service (IRS) [Member] | Delmarva Power & Light Company [Member]
Income Taxes [Line Items]
Current	(13)	29	(3)
Deferred	(20)	(21)	13
Investment Tax Credit	0	0	0
Internal Revenue Service (IRS) [Member] | Atlantic City Electric Company [Member]
Income Taxes [Line Items]
Current	(4)	(3)	(14)
Deferred	(43)	(6)	18
Investment Tax Credit	0	0	0
State and Local Jurisdiction [Member]
Income Taxes [Line Items]
Current	42	5	(1)
Deferred	177	267	16
State and Local Jurisdiction [Member] | Exelon Generation Co L L C [Member]
Income Taxes [Line Items]
Current	40	10	6
Deferred	(46)	82	(83)
State and Local Jurisdiction [Member] | Commonwealth Edison Co [Member]
Income Taxes [Line Items]
Current	(27)	(5)	(29)
Deferred	118	96	117
State and Local Jurisdiction [Member] | PECO Energy Co [Member]
Income Taxes [Line Items]
Current	0	0	1
Deferred	(24)	0	(16)
State and Local Jurisdiction [Member] | Baltimore Gas and Electric Company [Member]
Income Taxes [Line Items]
Current	0	0	0
Deferred	27	35	32
State and Local Jurisdiction [Member] | Pepco Holdings LLC [Member]
Income Taxes [Line Items]
Current	(5)	3	7
Deferred	33	27	8
State and Local Jurisdiction [Member] | Potomac Electric Power Company [Member]
Income Taxes [Line Items]
Current	0	0	0
Deferred	15	6	5
State and Local Jurisdiction [Member] | Delmarva Power & Light Company [Member]
Income Taxes [Line Items]
Current	0	0	0
Deferred	8	14	12
State and Local Jurisdiction [Member] | Atlantic City Electric Company [Member]
Income Taxes [Line Items]
Current	0	0	0
Deferred	$ 6	$ 9	$ 8