Variable Interest Entities - Carrying Amounts and Classification of Consolidated VIE Assets and Liabilities (Details) - USD ($) $ in Millions		Sep. 30, 2018	Dec. 31, 2017
Variable Interest Entity [Line Items]
Current assets	[1]	$ 891	$ 662
Noncurrent assets	[1]	9,259	9,317
Total assets	[1]	10,150	9,979
Current liabilities	[1]	329	308
Noncurrent liabilities	[1]	3,284	3,316
Total liabilities	[1]	3,613	3,624
Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Current assets		881	652
Noncurrent assets		9,233	9,286
Total assets		10,114	9,938
Current liabilities		303	272
Noncurrent liabilities		3,232	3,250
Total liabilities		3,535	3,522
Pepco Holdings LLC [Member]
Variable Interest Entity [Line Items]
Current assets	[1]	10	10
Noncurrent assets	[1]	26	31
Total assets	[1]	36	41
Current liabilities	[1]	26	36
Noncurrent liabilities	[1]	52	66
Total liabilities	[1]	78	102
Atlantic City Electric Company [Member]
Variable Interest Entity [Line Items]
Current assets		7	6
Noncurrent assets		19	23
Total assets		26	29
Current liabilities		23	32
Noncurrent liabilities		45	58
Total liabilities		$ 68	$ 90

[1] Includes certain purchase accounting adjustments not pushed down to the ACE standalone entity.