Debt and Credit Agreements - Summary of Credit Facility Thresholds (Details) - Exelon Generation Co L L C [Member] $ in Millions	Dec. 31, 2020 USD ($)
Line of credit
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 1,500
BilateralOct2012 [Member] | Line of credit
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	200
BilateralJan2013 [Member] | Line of credit
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	100
BilateralJan2016 [Member] | Line of credit
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	150
BilateralFeb2019 [Member] | Line of credit
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	100
BilateralOct2019a [Member] | Line of credit
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	200
BilateralOct2019b [Member] | Line of credit
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	100
BilateralNov2019a [Member] | Line of credit
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	300
BilateralNov2019b [Member] | Line of credit
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	150
BilateralNov2019c [Member] | Line of credit
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	100
ExGenBilat100May152020
Line of Credit Facility [Line Items]
Line of credit facility, fair value of amount outstanding	0
ExGenBilat100May152020 | Line of credit
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 100