Accounts Receivable Schedule of Estimated Unbilled Revenues (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unbilled customer revenues		$ 1,858	$ 1,673
Allowance for uncollectible accounts	[1]	(322)	(334)
Regulatory Assets		9,288	11,388
Exelon Generation Co L L C [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unbilled customer revenues	[2]	1,017	910
Allowance for uncollectible accounts	[1]	(114)	(91)
Commonwealth Edison Co [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unbilled customer revenues		242	219
Allowance for uncollectible accounts	[1]	(73)	(70)
Regulatory Assets		1,279	1,167
PECO Energy Co [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unbilled customer revenues		162	140
Allowance for uncollectible accounts	[1],[3]	(56)	(61)
Allowance for Doubtful Accounts Receivable, Noncurrent		15	23
Regulatory Assets		410	1,710
Baltimore Gas and Electric Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unbilled customer revenues		205	182
Allowance for uncollectible accounts	[1]	(24)	(32)
Regulatory Assets		571	712
Pepco Holdings LLC [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Charged to Costs and Expenses		10
Pepco Holdings LLC [Member] | Successor [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unbilled customer revenues		232	222
Allowance for uncollectible accounts	[1]	(55)	(80)	[4]
Regulatory Assets		3,047	3,504
Potomac Electric Power Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unbilled customer revenues		133	123
Allowance for uncollectible accounts	[1]	(21)	(29)	[4]
Regulatory Assets		891	852
Charged to Costs and Expenses		6
Delmarva Power and Light Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unbilled customer revenues		68	58
Allowance for uncollectible accounts	[1]	(16)	(24)	[4]
Regulatory Assets		314	348
Charged to Costs and Expenses		4
Atlantic City Electric Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unbilled customer revenues		31	41
Allowance for uncollectible accounts	[1]	(18)	(27)	[4]
Regulatory Assets		430	$ 501
PHI Merger [Member] | Pepco Holdings LLC [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for uncollectible accounts		(30)
Regulatory Assets		20
PHI Merger [Member] | Potomac Electric Power Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for uncollectible accounts		(14)
Regulatory Assets		8
PHI Merger [Member] | Delmarva Power and Light Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for uncollectible accounts		(8)
Regulatory Assets		4
PHI Merger [Member] | Atlantic City Electric Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for uncollectible accounts		(8)
Regulatory Assets		$ 8

[1] Includes the estimated allowance for uncollectible accounts on billed customer and other accounts receivable.

[2] Represents unbilled portion of retail receivables estimated under Exelon’s unbilled critical accounting policy.

[3] Excludes the non-current allowance for uncollectible accounts of $15 million and $23 million at December 31, 2017 and 2016, respectively, related to PECO’s current installment plan receivables described below.

[4] At December 31, 2016, as explained in Note 1 — Significant Accounting Policies, PHI, Pepco, DPL and ACE estimated the allowance for uncollectible accounts on customer receivables by applying loss rates to the outstanding receivable balance by risk segment. The change in estimate resulted in an overall increase of $30 million, $14 million, $8 million, and $8 million in the allowance for uncollectible accounts with $20 million, $8 million, $4 million, and $8 million deferred as a regulatory asset on PHI's, Pepco's, DPL's and ACE's Consolidated Balance Sheets at December 31, 2016, respectively. This also resulted in a $10 million, $6 million, and $4 million pre-tax charge to provision for uncollectible accounts expense for the year ended December 31, 2016, which is included in Operating and maintenance expense on PHI's, Pepco's and DPL's Consolidated Statements of Operations and Comprehensive Income, respectively.