Variable Interest Entities - Carrying Amounts and Classification of Consolidated VIE Assets and Liabilities (Details) - USD ($) $ in Millions		Jun. 30, 2017	Dec. 31, 2016
Variable Interest Entity [Line Items]
Consolidated VIE Assets	[1],[2]	$ 9,129	$ 9,517
Consolidated VIE Liabilities	[1],[2]	3,296	3,598
Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Consolidated VIE Assets		9,086	9,441
Consolidated VIE Liabilities		3,175	3,414
Baltimore Gas and Electric Company [Member]
Variable Interest Entity [Line Items]
Consolidated VIE Assets			26
Consolidated VIE Liabilities			42
Pepco Holdings LLC [Member] | Successor [Member]
Variable Interest Entity [Line Items]
Consolidated VIE Assets	[1]	43	49
Consolidated VIE Liabilities	[1]	121	143
Atlantic City Electric Company [Member]
Variable Interest Entity [Line Items]
Consolidated VIE Assets		30	32
Consolidated VIE Liabilities		108	126
CurrentAssetsMember [Member]
Variable Interest Entity [Line Items]
Consolidated VIE Assets	[1],[2]	512	954
CurrentAssetsMember [Member] | Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Consolidated VIE Assets		501	916
CurrentAssetsMember [Member] | Baltimore Gas and Electric Company [Member]
Variable Interest Entity [Line Items]
Consolidated VIE Assets			23
CurrentAssetsMember [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Variable Interest Entity [Line Items]
Consolidated VIE Assets	[1]	11	14
CurrentAssetsMember [Member] | Atlantic City Electric Company [Member]
Variable Interest Entity [Line Items]
Consolidated VIE Assets		7	9
NoncurrentAssetMember [Member]
Variable Interest Entity [Line Items]
Consolidated VIE Assets	[1],[2]	8,617	8,563
NoncurrentAssetMember [Member] | Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Consolidated VIE Assets		8,585	8,525
NoncurrentAssetMember [Member] | Baltimore Gas and Electric Company [Member]
Variable Interest Entity [Line Items]
Consolidated VIE Assets			3
NoncurrentAssetMember [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Variable Interest Entity [Line Items]
Consolidated VIE Assets	[1]	32	35
NoncurrentAssetMember [Member] | Atlantic City Electric Company [Member]
Variable Interest Entity [Line Items]
Consolidated VIE Assets		23	23
CurrentLiabilityMember [Member]
Variable Interest Entity [Line Items]
Consolidated VIE Liabilities	[1],[2]	573	885
CurrentLiabilityMember [Member] | Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Consolidated VIE Liabilities		535	802
CurrentLiabilityMember [Member] | Baltimore Gas and Electric Company [Member]
Variable Interest Entity [Line Items]
Consolidated VIE Liabilities			42
CurrentLiabilityMember [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Variable Interest Entity [Line Items]
Consolidated VIE Liabilities	[1]	38	42
CurrentLiabilityMember [Member] | Atlantic City Electric Company [Member]
Variable Interest Entity [Line Items]
Consolidated VIE Liabilities		34	37
NoncurrentLiabilityMember [Member]
Variable Interest Entity [Line Items]
Consolidated VIE Liabilities	[1],[2]	2,723	2,713
NoncurrentLiabilityMember [Member] | Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Consolidated VIE Liabilities		2,640	2,612
NoncurrentLiabilityMember [Member] | Baltimore Gas and Electric Company [Member]
Variable Interest Entity [Line Items]
Consolidated VIE Liabilities			0
NoncurrentLiabilityMember [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Variable Interest Entity [Line Items]
Consolidated VIE Liabilities	[1]	83	101
NoncurrentLiabilityMember [Member] | Atlantic City Electric Company [Member]
Variable Interest Entity [Line Items]
Consolidated VIE Liabilities		$ 74	$ 89

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

[2] Includes certain purchase accounting adjustments not pushed down to the BGE standalone entity.