Stock-Based Compensation Plans - Components of Tax Benefits from Stock-based Compensation (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Common Stock [Abstract]
Restricted stock units	$ 30	$ 17	$ 11
Performance share awards	18	11	11
Stock deferral plan	$ 0	$ 0	$ 1

Reductions in the entity's income taxes that arise when compensation cost (from non-qualified performance share awards) recognized on the entity's tax return exceeds compensation cost from non-qualified performance share awards recognized on the income statement. This element increases net cash provided by operating activities.

No definition available.

Name:	exc_TaxBenefitFromPerformanceShareAwardsDistributed
Namespace Prefix:	exc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration