Variable Interest Entities - Carrying Amounts and Classification of Consolidated VIE Assets and Liabilities (Details) - USD ($) $ in Millions		Sep. 30, 2017	Dec. 31, 2016
Variable Interest Entity [Line Items]
Current assets	[1]	$ 657	$ 954	[2]
Noncurrent assets	[1]	9,252	8,563	[2]
Total assets	[1]	9,909	9,517	[2]
Current liabilities	[1]	404	885	[2]
Noncurrent liabilities	[1]	3,290	2,713	[2]
Total liabilities	[1]	3,694	3,598	[2]
Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Current assets		644	916
Noncurrent assets		9,222	8,525
Total assets		9,866	9,441
Current liabilities		367	802
Noncurrent liabilities		3,215	2,612
Total liabilities		3,582	3,414
Baltimore Gas and Electric Company [Member]
Variable Interest Entity [Line Items]
Current assets			23
Noncurrent assets			3
Total assets			26
Current liabilities			42
Noncurrent liabilities			0
Total liabilities			42
Pepco Holdings LLC [Member] | Successor [Member]
Variable Interest Entity [Line Items]
Current assets	[1]	13	14
Noncurrent assets	[1]	30	35
Total assets	[1]	43	49
Current liabilities	[1]	37	42
Noncurrent liabilities	[1]	75	101
Total liabilities	[1]	112	143
Atlantic City Electric Company [Member]
Variable Interest Entity [Line Items]
Current assets		9	9
Noncurrent assets		22	23
Total assets		31	32
Current liabilities		33	37
Noncurrent liabilities		67	89
Total liabilities		$ 100	$ 126

[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.