Income Taxes - Summary of Interest Receivable (Payable) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Income Taxes [Line Items]
Net Interest Receivable Payable Related To Uncertain Tax Positions	$ 314	$ 318

The amount of net interest receivable (payable) recognized for uncertain tax positions as of the balance sheet date.

No definition available.

Name:	exc_NetInterestReceivablePayableRelatedToUncertainTaxPositions
Namespace Prefix:	exc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant