Mergers, Acquisitions, and Dispositions Purchase Price Allocation Table - PHI (Details) - Pepco Holdings LLC [Member] $ in Millions	Mar. 23, 2016 USD ($)
Business Acquisition [Line Items]
Current assets	$ 1,441	[1]
Property, plant and equipment	11,088	[1]
Regulatory assets	5,015	[1]
Other assets	248	[1]
Goodwill	4,005
Total assets	21,797	[1]
Current liabilities	2,752	[1]
Unamortized energy contracts	1,515	[1]
Regulatory liabilities	297	[1]
Long-term debt, including current maturities	5,636	[1]
Deferred income taxes	3,447	[1]
Pension and OPEB obligations	821	[1]
Other liabilities	187	[1]
Total liabilities	14,655	[1]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net	$ 7,142	[1]

[1] Amounts shown reflect the final purchase price allocation and the correction of a reporting error identified and corrected in the second quarter of 2016. The error had resulted in a gross up of certain assets and liabilities related to legacy PHI intercompany and income tax receivable and payable balances.