Variable Interest Entities - Carrying Amounts and Classification of Consolidated VIE Assets and Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Variable Interest Entity [Line Items]
Variable Interest Entity, Consolidated, Carrying Amount, Assets	$ 9,517	$ 8,918
Variable Interest Entity, Consolidated, Carrying Amount, Liabilities	3,598	3,400
CurrentAssetsMember [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Consolidated, Carrying Amount, Assets	954	909
NoncurrentAssetMember [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Consolidated, Carrying Amount, Assets	8,563	8,009
CurrentLiabilityMember [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Consolidated, Carrying Amount, Liabilities	885	473
NoncurrentLiabilityMember [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Consolidated, Carrying Amount, Liabilities	2,713	2,927
Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Consolidated, Carrying Amount, Assets	9,441	8,885
Variable Interest Entity, Consolidated, Carrying Amount, Liabilities	3,414	3,271
Exelon Generation Co L L C [Member] | CurrentAssetsMember [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Consolidated, Carrying Amount, Assets	916	881
Exelon Generation Co L L C [Member] | NoncurrentAssetMember [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Consolidated, Carrying Amount, Assets	8,525	8,004
Exelon Generation Co L L C [Member] | CurrentLiabilityMember [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Consolidated, Carrying Amount, Liabilities	802	387
Exelon Generation Co L L C [Member] | NoncurrentLiabilityMember [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Consolidated, Carrying Amount, Liabilities	2,612	2,884
Pepco Holdings LLC [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Consolidated, Carrying Amount, Assets	49	30
Variable Interest Entity, Consolidated, Carrying Amount, Liabilities	143	172
Pepco Holdings LLC [Member] | Predecessor [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Consolidated, Carrying Amount, Assets		30
Variable Interest Entity, Consolidated, Carrying Amount, Liabilities		172
Pepco Holdings LLC [Member] | Predecessor [Member] | CurrentAssetsMember [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Consolidated, Carrying Amount, Assets		12
Pepco Holdings LLC [Member] | Predecessor [Member] | NoncurrentAssetMember [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Consolidated, Carrying Amount, Assets		18
Pepco Holdings LLC [Member] | Predecessor [Member] | CurrentLiabilityMember [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Consolidated, Carrying Amount, Liabilities		48
Pepco Holdings LLC [Member] | Predecessor [Member] | NoncurrentLiabilityMember [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Consolidated, Carrying Amount, Liabilities		124
Pepco Holdings LLC [Member] | Successor [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Consolidated, Carrying Amount, Assets	49
Variable Interest Entity, Consolidated, Carrying Amount, Liabilities	143
Pepco Holdings LLC [Member] | Successor [Member] | CurrentAssetsMember [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Consolidated, Carrying Amount, Assets	14
Pepco Holdings LLC [Member] | Successor [Member] | NoncurrentAssetMember [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Consolidated, Carrying Amount, Assets	35
Pepco Holdings LLC [Member] | Successor [Member] | CurrentLiabilityMember [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Consolidated, Carrying Amount, Liabilities	42
Pepco Holdings LLC [Member] | Successor [Member] | NoncurrentLiabilityMember [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Consolidated, Carrying Amount, Liabilities	101
Atlantic City Electric Company [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Consolidated, Carrying Amount, Assets	32	30
Variable Interest Entity, Consolidated, Carrying Amount, Liabilities	126	172
Atlantic City Electric Company [Member] | CurrentAssetsMember [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Consolidated, Carrying Amount, Assets	9	12
Atlantic City Electric Company [Member] | NoncurrentAssetMember [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Consolidated, Carrying Amount, Assets	23	18
Atlantic City Electric Company [Member] | CurrentLiabilityMember [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Consolidated, Carrying Amount, Liabilities	37	48
Atlantic City Electric Company [Member] | NoncurrentLiabilityMember [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Consolidated, Carrying Amount, Liabilities	89	124
Baltimore Gas and Electric Company [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Consolidated, Carrying Amount, Assets	26	26
Variable Interest Entity, Consolidated, Carrying Amount, Liabilities	42	122
Baltimore Gas and Electric Company [Member] | CurrentAssetsMember [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Consolidated, Carrying Amount, Assets	23	23
Baltimore Gas and Electric Company [Member] | NoncurrentAssetMember [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Consolidated, Carrying Amount, Assets	3	3
Baltimore Gas and Electric Company [Member] | CurrentLiabilityMember [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Consolidated, Carrying Amount, Liabilities	42	81
Baltimore Gas and Electric Company [Member] | NoncurrentLiabilityMember [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Consolidated, Carrying Amount, Liabilities	$ 0	$ 41