Variable Interest Entities - Assets and Liabilities of VIES which Creditors or Beneficiaries have no Recourse (Details) - USD ($) $ in Millions		Mar. 31, 2016	Dec. 31, 2015		Mar. 31, 2015	Dec. 31, 2014
Variable Interest Entity [Line Items]
Cash and cash equivalents		$ 960	$ 6,502		$ 1,825	$ 1,878
Restricted cash		218	205
Accounts receivable, net
Customer		3,594	3,187
Other		1,138	912
Derivative Asset, Current		1,185	1,365
Inventory
Materials and supplies		1,229	1,104
Other current assets		1,086	752
Total current assets		11,364	15,334
Property, plant and equipment, net		69,406	57,439
Nuclear decommissioning trust funds		10,526	10,342
Goodwill		6,688	2,672
Derivative Asset, Noncurrent		841	758
Other noncurrent assets		1,398	1,445
Total assets		111,742	95,384
Short-term borrowings		3,640	533
Long-term debt due within one year		2,058	1,500
Accounts payable		2,874	2,883
Accrued expenses		2,260	2,376
Mark-to-market derivative liabilities (current liabilities)		203	205
Other current liabilities		582	100
Other		1,008	842
Total current liabilities		13,770	9,118
Long-term debt		29,314	23,645
Asset retirement obligations		8,755	8,585
Pension obligation(c)		3,771	3,385
Energy Marketing Contract Liabilities, Noncurrent		1,144	117
Other noncurrent liabilities		1,886	1,491
Total deferred credits and other liabilities		40,812	34,658
Total liabilities	[1]	84,537	68,062
Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		145	164
Restricted cash		117	100
Accounts receivable, net
Customer		231	219
Other		28	43
Derivative Asset, Current		120	140
Inventory
Materials and supplies		186	181
Other current assets		50	35
Total current assets		877	882
Property, plant and equipment, net		5,141	5,160
Nuclear decommissioning trust funds		2,069	2,036
Goodwill		47	47
Derivative Asset, Noncurrent		41	53
Other noncurrent assets		135	90
Total noncurrent assets		7,433	7,386
Total assets		8,310	8,268
Long-term debt due within one year		265	111
Accounts payable		164	216
Accrued expenses		81	115
Mark-to-market derivative liabilities (current liabilities)		7	5
Other current liabilities		12	12
Other		13	13
Total current liabilities		542	472
Long-term debt		743	666
Asset retirement obligations	[2]	2,016	1,999
Pension obligation(c)		9	9
Energy Marketing Contract Liabilities, Noncurrent		35	39
Other noncurrent liabilities		76	79
Total deferred credits and other liabilities		2,879	2,792
Total liabilities		3,421	3,264
Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		377	431		532	780
Restricted cash		119	123
Accounts receivable, net
Customer		1,963	2,095
Other		434	360
Derivative Asset, Current		1,185	1,365
Inventory
Materials and supplies		884	880
Other current assets		719	535
Total current assets		6,171	6,342
Property, plant and equipment, net		26,166	25,843
Nuclear decommissioning trust funds		10,526	10,342
Goodwill		47	47
Derivative Asset, Noncurrent		799	733
Other noncurrent assets		650	627
Total assets		47,002	46,529
Short-term borrowings		1,529	29
Long-term debt due within one year		177	90
Accounts payable		1,290	1,583
Accrued expenses		673	935
Mark-to-market derivative liabilities (current liabilities)		177	182
Other current liabilities		85	100
Other		333	356
Total current liabilities		4,775	4,933
Long-term debt		7,945	7,936
Asset retirement obligations		8,588	8,431
Energy Marketing Contract Liabilities, Noncurrent		106	117
Other noncurrent liabilities		637	602
Total deferred credits and other liabilities		19,999	19,757
Total liabilities	[3]	33,649	33,559
Exelon Generation Co L L C [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		145	164
Restricted cash		62	77
Accounts receivable, net
Customer		231	219
Other		28	43
Derivative Asset, Current		120	140
Inventory
Materials and supplies		186	181
Other current assets		36	30
Total current assets		808	854
Property, plant and equipment, net		5,141	5,160
Nuclear decommissioning trust funds		2,069	2,036
Goodwill		47	47
Derivative Asset, Noncurrent		41	53
Other noncurrent assets		84	85
Total noncurrent assets		7,382	7,381
Total assets		8,190	8,235
Long-term debt due within one year		128	27
Accounts payable		164	216
Accrued expenses		75	113
Mark-to-market derivative liabilities (current liabilities)		7	5
Other current liabilities		12	12
Other		13	13
Total current liabilities		399	386
Long-term debt		559	623
Asset retirement obligations		2,016	1,999	[2]
Pension obligation(c)		9	9
Energy Marketing Contract Liabilities, Noncurrent		35	39
Other noncurrent liabilities		76	79
Total deferred credits and other liabilities		2,695	2,749
Total liabilities		3,094	3,135
Baltimore Gas and Electric Company [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		5	9		41	64
Restricted cash		44	24
Accounts receivable, net
Customer		328	300
Other		77	112
Inventory
Materials and supplies		39	33
Other current assets		16	3
Total current assets		819	845
Property, plant and equipment, net		6,684	6,597
Other noncurrent assets		10	8
Total assets		8,361	8,295
Short-term borrowings		150	210
Long-term debt due within one year		378	378
Accounts payable		206	209
Accrued expenses		151	110
Other		28	35
Total current liabilities		1,138	1,134
Long-term debt		1,481	1,480
Asset retirement obligations		15	17
Other noncurrent liabilities		71	61
Total deferred credits and other liabilities		2,546	2,552
Total liabilities	[4]	5,417	5,418
Baltimore Gas and Electric Company [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		0	0
Restricted cash		44	23
Accounts receivable, net
Customer		0	0
Other		0	0
Derivative Asset, Current		0	0
Inventory
Materials and supplies		0	0
Other current assets		0	0
Total current assets		44	23
Property, plant and equipment, net		0	0
Nuclear decommissioning trust funds		0	0
Goodwill		0	0
Derivative Asset, Noncurrent		0	0
Other noncurrent assets		3	3
Total noncurrent assets		3	3
Total assets		47	26
Long-term debt due within one year		79	79
Accounts payable		0	0
Accrued expenses		4	2
Mark-to-market derivative liabilities (current liabilities)		0	0
Other current liabilities		0	0
Other		0	0
Total current liabilities		83	81
Long-term debt		41	41
Asset retirement obligations		0	0
Pension obligation(c)	[2]	0	0
Energy Marketing Contract Liabilities, Noncurrent		0	0
Other noncurrent liabilities		0	0
Total deferred credits and other liabilities		41	41
Total liabilities		124	122
PEPCO Holdings Inc [Member]
Accounts receivable, net
Derivative Asset, Current			18
Inventory
Derivative Asset, Noncurrent			0
Mark-to-market derivative liabilities (current liabilities)			0
PEPCO Holdings Inc [Member] | Variable Interest Entity, Primary Beneficiary [Member] | Predecessor [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents			0
Restricted cash			12
Accounts receivable, net
Customer			0
Other			0
Derivative Asset, Current			0
Inventory
Materials and supplies			0
Other current assets			0
Total current assets			12
Property, plant and equipment, net			0
Nuclear decommissioning trust funds			0
Goodwill			0
Derivative Asset, Noncurrent			0
Other noncurrent assets			18
Total noncurrent assets			18
Total assets			30
Long-term debt due within one year			46
Accounts payable			0
Accrued expenses			2
Mark-to-market derivative liabilities (current liabilities)			0
Other current liabilities			0
Other			0
Total current liabilities			48
Long-term debt			124
Asset retirement obligations			0
Pension obligation(c)	[2]		0
Energy Marketing Contract Liabilities, Noncurrent			0
Other noncurrent liabilities			0
Total deferred credits and other liabilities			124
Total liabilities			172
PEPCO Holdings Inc [Member] | Variable Interest Entity, Primary Beneficiary [Member] | Successor [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		0
Restricted cash		11
Accounts receivable, net
Customer		0
Other		0
Derivative Asset, Current		0
Inventory
Materials and supplies		0
Other current assets		11
Total current assets		22
Property, plant and equipment, net		0
Nuclear decommissioning trust funds		0
Goodwill		0
Derivative Asset, Noncurrent		0
Other noncurrent assets		46
Total noncurrent assets		46
Total assets		68
Long-term debt due within one year		56
Accounts payable		0
Accrued expenses		2
Mark-to-market derivative liabilities (current liabilities)		0
Other current liabilities		0
Other		0
Total current liabilities		58
Long-term debt		142
Asset retirement obligations		0
Pension obligation(c)	[2]	0
Energy Marketing Contract Liabilities, Noncurrent		0
Other noncurrent liabilities		0
Total deferred credits and other liabilities		142
Total liabilities		200
Atlantic City Electric Company [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		122	3		$ 6	$ 2
Restricted cash		11	12
Accounts receivable, net
Customer		146	156
Other		74	242
Inventory
Materials and supplies		24	23
Other current assets		13	12
Total current assets		485	546
Property, plant and equipment, net		2,384	2,322
Other noncurrent assets		22	19
Total assets		3,393	3,387
Short-term borrowings		0	5
Long-term debt due within one year		47	48
Accounts payable		101	96
Accrued expenses		77	70
Other		16	14
Total current liabilities		444	297
Long-term debt		1,144	1,153
Other noncurrent liabilities		22	12
Total deferred credits and other liabilities		916	937
Total liabilities		2,504	2,387
Atlantic City Electric Company [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		0	0
Restricted cash		11	12
Accounts receivable, net
Customer		0	0
Other		0	0
Derivative Asset, Current		0	0
Inventory
Materials and supplies		0	0
Other current assets		0	0
Total current assets		11	12
Property, plant and equipment, net		0	0
Nuclear decommissioning trust funds		0	0
Goodwill		0	0
Derivative Asset, Noncurrent		0	0
Other noncurrent assets		18	18
Total noncurrent assets		18	18
Total assets		29	30
Long-term debt due within one year		45	46
Accounts payable		0	0
Accrued expenses		2	2
Mark-to-market derivative liabilities (current liabilities)		0	0
Other current liabilities		0	0
Other		0	0
Total current liabilities		47	48
Long-term debt		114	124
Asset retirement obligations		0	0
Pension obligation(c)	[2]	0	0
Energy Marketing Contract Liabilities, Noncurrent		0	0
Other noncurrent liabilities		0	0
Total deferred credits and other liabilities		114	124
Total liabilities		$ 161	$ 172

[1] Exelon’s consolidated assets include $8,310 million and $8,268 million at March 31, 2016 and December 31, 2015, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Exelon’s consolidated liabilities include $3,421 million and $3,264 million at March 31, 2016 and December 31, 2015, respectively, of certain VIEs for which the VIE creditors do not have recourse to Exelon. See Note 3 - Variable Interest Entities.

[2] Includes the CNEG retail gas pension obligation, which is presented as a net asset balance within the Prepaid pension asset line item on Generation’s balance sheet. See Note 13 - Retirement Benefits for additional details.

[3] Generation’s consolidated assets include $8,190 million and $8,235 million at March 31, 2016 and December 31, 2015, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Generation’s consolidated liabilities include $3,094 million and $3,135 million at March 31, 2016 and December 31, 2015, respectively, of certain VIEs for which the VIE creditors do not have recourse to Generation. See Note 3 - Variable Interest Entities.

[4] BGE’s consolidated assets include $47 million and $26 million at March 31, 2016 and December 31, 2015, respectively, of BGE’s consolidated VIE that can only be used to settle the liabilities of the VIE. BGE’s consolidated liabilities include $41 million and $41 million at March 31, 2016 and December 31, 2015, respectively, of BGE’s consolidated VIE for which the VIE creditors do not have recourse to BGE. See Note 3 - Variable Interest Entities.