Regulatory Matters - Estimated Commitments related to PJM Agreements (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Other Commitments [Line Items]
Other Receivables	$ 1,583	$ 1,256
Accounts Payable, Current	3,560	3,800
Regulatory Assets	9,505	9,427
Regulatory Liabilities	10,392	10,203
Exelon Generation Co L L C [Member]
Other Commitments [Line Items]
Other Receivables	619	562
Accounts Payable, Current	1,692	1,847
Commonwealth Edison Co [Member]
Other Commitments [Line Items]
Other Receivables	286	320
Accounts Payable, Current	527	607
Regulatory Assets	1,761	1,600
Regulatory Liabilities	6,742	6,343
PECO Energy Co [Member]
Other Commitments [Line Items]
Other Receivables	138	151
Accounts Payable, Current	387	370
Regulatory Assets	595	541
Regulatory Liabilities	601	596
Baltimore Gas and Electric Company [Member]
Other Commitments [Line Items]
Other Receivables	147	90
Accounts Payable, Current	243	295
Regulatory Assets	637	575
Regulatory Liabilities	1,228	1,269
Pepco Holdings LLC [Member]
Other Commitments [Line Items]
Other Receivables	174	177
Accounts Payable, Current	462	496
Regulatory Assets	2,473	2,769
Regulatory Liabilities	1,777	1,948
Potomac Electric Power Company [Member]
Other Commitments [Line Items]
Other Receivables	91	81
Accounts Payable, Current	195	214
Regulatory Assets	772	881
Regulatory Liabilities	754	829
Delmarva Power & Light Company [Member]
Other Commitments [Line Items]
Other Receivables	38	46
Accounts Payable, Current	112	111
Regulatory Assets	274	290
Regulatory Liabilities	611	665
Atlantic City Electric Company [Member]
Other Commitments [Line Items]
Other Receivables	48	55
Accounts Payable, Current	144	154
Regulatory Assets	425	426
Regulatory Liabilities	$ 382	420
PJM Transmission Rate Design Settlement [Member]
Other Commitments [Line Items]
Other Receivables		220
Accounts Payable, Current		176
PJM Transmission Rate Design Settlement [Member] | Exelon Generation Co L L C [Member]
Other Commitments [Line Items]
Other Receivables		0
Accounts Payable, Current		41
Accounts Receivable, before Allowance for Credit Loss, Current		16
PJM Transmission Rate Design Settlement [Member] | Commonwealth Edison Co [Member]
Other Commitments [Line Items]
Other Receivables		122
Accounts Payable, Current		0
PJM Transmission Rate Design Settlement [Member] | PECO Energy Co [Member]
Other Commitments [Line Items]
Other Receivables		85
Accounts Payable, Current		0
PJM Transmission Rate Design Settlement [Member] | Baltimore Gas and Electric Company [Member]
Other Commitments [Line Items]
Other Receivables		0
Accounts Payable, Current		51
PJM Transmission Rate Design Settlement [Member] | Pepco Holdings LLC [Member]
Other Commitments [Line Items]
Other Receivables		13
Accounts Payable, Current		84
PJM Transmission Rate Design Settlement [Member] | Potomac Electric Power Company [Member]
Other Commitments [Line Items]
Other Receivables		0
Accounts Payable, Current		84
PJM Transmission Rate Design Settlement [Member] | Delmarva Power & Light Company [Member]
Other Commitments [Line Items]
Other Receivables		10
Accounts Payable, Current		0
PJM Transmission Rate Design Settlement [Member] | Atlantic City Electric Company [Member]
Other Commitments [Line Items]
Other Receivables		3
Accounts Payable, Current		0
PJM Transmission Rate Design Settlement [Member]
Other Commitments [Line Items]
Regulatory Assets		136
PJM Transmission Rate Design Settlement [Member] | Exelon Generation Co L L C [Member]
Other Commitments [Line Items]
Regulatory Assets		0
PJM Transmission Rate Design Settlement [Member] | Commonwealth Edison Co [Member]
Other Commitments [Line Items]
Regulatory Assets		0
PJM Transmission Rate Design Settlement [Member] | PECO Energy Co [Member]
Other Commitments [Line Items]
Regulatory Assets		0
PJM Transmission Rate Design Settlement [Member] | Baltimore Gas and Electric Company [Member]
Other Commitments [Line Items]
Regulatory Assets		51
PJM Transmission Rate Design Settlement [Member] | Pepco Holdings LLC [Member]
Other Commitments [Line Items]
Regulatory Assets		85
PJM Transmission Rate Design Settlement [Member] | Potomac Electric Power Company [Member]
Other Commitments [Line Items]
Regulatory Assets		84
PJM Transmission Rate Design Settlement [Member] | Delmarva Power & Light Company [Member]
Other Commitments [Line Items]
Regulatory Assets		0
PJM Transmission Rate Design Settlement [Member] | Atlantic City Electric Company [Member]
Other Commitments [Line Items]
Regulatory Assets		1
PJM Transmission Rate Design Settlement [Member]
Other Commitments [Line Items]
Regulatory Liabilities		221
PJM Transmission Rate Design Settlement [Member] | Exelon Generation Co L L C [Member]
Other Commitments [Line Items]
Regulatory Liabilities		0
PJM Transmission Rate Design Settlement [Member] | Commonwealth Edison Co [Member]
Other Commitments [Line Items]
Regulatory Liabilities		122
PJM Transmission Rate Design Settlement [Member] | PECO Energy Co [Member]
Other Commitments [Line Items]
Regulatory Liabilities		85
PJM Transmission Rate Design Settlement [Member] | Baltimore Gas and Electric Company [Member]
Other Commitments [Line Items]
Regulatory Liabilities		0
PJM Transmission Rate Design Settlement [Member] | Pepco Holdings LLC [Member]
Other Commitments [Line Items]
Regulatory Liabilities		14
PJM Transmission Rate Design Settlement [Member] | Potomac Electric Power Company [Member]
Other Commitments [Line Items]
Regulatory Liabilities		0
PJM Transmission Rate Design Settlement [Member] | Delmarva Power & Light Company [Member]
Other Commitments [Line Items]
Regulatory Liabilities		10
PJM Transmission Rate Design Settlement [Member] | Atlantic City Electric Company [Member]
Other Commitments [Line Items]
Regulatory Liabilities		$ 4