Mergers, Acquisitions, and Dispositions ProForma Impact of Merger (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended				12 Months Ended
	Jun. 30, 2016		Jun. 30, 2017	[3],[4]	Jun. 30, 2016		Dec. 31, 2016
Business Acquisition, Pro Forma Revenue	$ 6,910	[1]			$ 15,466	[1]	$ 32,342	[2]
Business Acquisition, Pro Forma Net Income (Loss)	$ 268	[1]			$ 845	[1]	$ 1,562	[2]
Business Acquisition, Pro Forma Earnings Per Share, Basic	$ 0.29	[1]			$ 0.92	[1]	$ 1.69	[2]
Business Acquisition, Pro Forma Earnings Per Share, Diluted	$ 0.29	[1]			$ 0.91	[1]	$ 1.69	[2]
Noncash Merger Related Costs			$ 0		$ 503
Pepco Holdings LLC [Member]
Noncash Merger Related Costs	$ 1				641		$ 680
Pepco Holdings LLC [Member] | Consolidation, Eliminations [Member]
Business Acquisition, Pro Forma Revenue					$ 170		$ 171

[1] The amounts above include adjustments for non-recurring costs directly related to the merger of $1 million and $641 million for the three and six months ended June 30, 2016, respectively, and intercompany revenue of $170 million for the six months ended June 30, 2016.

[2] The amounts above include adjustments for non-recurring costs directly related to the merger of $680 million and intercompany revenue of $171 million for the year ended December 31, 2016.

[3] Excludes $5 million of forgiveness of Accounts receivable related to merger commitments recorded in connection with the PHI Merger, the balance is included within Provision for uncollectible accounts.

[4] See Note 4 — Mergers, Acquisitions and Dispositions for additional information related to the merger with PHI.