Variable Interest Entities Variable Interest Entities - Carrying Amounts and Classification of Consolidated VIE Assets and Liabilities (Details) - USD ($) $ in Millions		Dec. 31, 2017	Dec. 31, 2016
Variable Interest Entity [Line Items]
Current assets	[1]	$ 630	$ 954	[2]
Noncurrent assets	[1]	9,317	8,563	[2]
Total assets	[1]	9,947	9,517	[2]
Current liabilities	[1]	306	885	[2]
Noncurrent liabilities	[1]	3,312	2,713	[2]
Total liabilities	[1]	3,618	3,598	[2]
Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Current assets		620	916
Noncurrent assets		9,286	8,525
Total assets		9,906	9,441
Current liabilities		270	802
Noncurrent liabilities		3,246	2,612
Total liabilities		3,516	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]
Variable Interest Entity [Line Items]
Total assets		41	49
Total liabilities		102	143
Pepco Holdings LLC [Member] | Successor [Member]
Variable Interest Entity [Line Items]
Current assets	[1]	10	14
Noncurrent assets	[1]	31	35
Total assets	[1]	41	49
Current liabilities	[1]	36	42
Noncurrent liabilities	[1]	66	101
Total liabilities	[1]	102	143
Atlantic City Electric Company [Member]
Variable Interest Entity [Line Items]
Current assets		6	9
Noncurrent assets		23	23
Total assets		29	32
Current liabilities		32	37
Noncurrent liabilities		58	89
Total liabilities		$ 90	$ 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.