Derivative Financial Instruments - Summary of Cash Collateral and Letters of Credit (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, Collateral, Right to Reclaim Cash	$ 713	$ 511
Derivative, Collateral, Right to Reclaim Securities	755	226
Derivative, Collateral, Obligation to Return Cash	182	110
Derivative, Collateral, Obligation to Return Securities	124	40
Incremental Collateral For Loss Of Investment Grade Credit Rating	2,113	1,432
Exelon Generation Co L L C [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, Collateral, Right to Reclaim Cash	713	511
Derivative, Collateral, Right to Reclaim Securities	755	226
Derivative, Collateral, Obligation to Return Cash	182	110
Derivative, Collateral, Obligation to Return Securities	124	40
Incremental Collateral For Loss Of Investment Grade Credit Rating	$ 2,113	$ 1,432