Stock-Based Compensation Plans - Balance Sheet Classification of Obligations related to Outstanding Performance Share Awards Not Yet Settled (Details) - USD ($) $ in Millions		Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Current liabilities	[1]	$ 49	$ 28	[2]
Deferred credits and other liabilities	[3]	52	32	[2]
Common stock		40	35	[2]
Total		$ 141	95	[2]
Pepco Holdings LLC [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock			$ 8

[1] Represents the current liability related to performance share awards expected to be settled in cash.

[2] Excludes $8 million of common stock for PHI at December 31, 2015

[3] Represents the long-term liability related to performance share awards expected to be settled in cash.