Consolidated Balance Sheets (Unaudited) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013		Dec. 31, 2012
Current assets
Cash and cash equivalents	$ 679		$ 1,411
Cash and cash equivalents of variable interest entities	93		75
Restricted cash and investments	83		86
Restricted cash and investments of variable interest entity	65		47
Accounts receivable, net
Customer	2,835		2,789
Other	1,110		1,147
Accounts receivable of variable interest entities	285		292
Mark-to-market derivative assets	666		938
Unamortized energy contracts assets	727		886
Inventories, net
Fossil fuel	122		246
Materials and supplies	791		768
Deferred income taxes	331		131
Regulatory assets	765		764
Other	722		560
Total current assets	9,274		10,140
Property, plant and equipment, net	45,784		45,186
Deferred debits and other assets
Regulatory assets	6,521		6,497
Nuclear decommissioning trust funds	7,559		7,248
Investments	1,181		1,184
Investments in affiliates	22		22
Investment in CENG	1,883		1,849
Goodwill	2,625		2,625
Mark-to-market derivative assets	706		937
Pledged assets for Zion Station decommissioning	580		614
Unamortized energy contracts assets	968		1,073
Other	1,140		1,186
Deferred income taxes	0		0
Total deferred debits and other assets	23,185		23,235
Total assets	78,243		78,561
Current liabilities
Short-term borrowings	233		0
Short-term notes payable - accounts receivable agreement	210		210
Long-term debt due within one year	2,085		975
Long-term debt of variable interest entities due within one year	79		72
Accounts payable	2,198		2,446
Accounts payable of variable interest entities	188		202
Accrued expenses	1,430		1,800
Deferred income taxes	29		58
Regulatory liabilities	418		368
Dividends payable	1		4
Mark-to-market derivative liabilities	181		352
Unamortized energy contract liabilities	410		455
Other	859		849
Total current liabilities	8,321		7,791
Long-term debt	16,210		17,190
Long-term debt of variable financing trusts	648		648
Long-term debt of variable interest entity	497		508
Deferred credits and other liabilities
Deferred income taxes and unamortized investment tax credits	11,315		11,551
Asset retirement obligations	5,149		5,074
Pension obligations	3,161		3,428
Non-pension postretirement benefit obligations	2,672		2,662
Spent nuclear fuel obligation	1,020		1,020
Regulatory liabilities	4,115		3,981
Mark-to-market derivative liabilities	259		281
Unamortized energy contract liabilities	466		528
Payable for Zion Station decommissioning	372		432
Other	2,625		1,650
Total deferred credits and other liabilities	31,154		30,607
Total liabilities	56,830		56,744
Commitments and contingencies
Preferred securities	87		87
Shareholders' equity
Common stock	16,652		16,632
Treasury stock, at cost (35 and 35 shares held at December 31, 2010 and December 31, 2009, respectively)	(2,327)		(2,327)
Retained earnings	9,437		9,893
Accumulated other comprehensive income (loss), net	(2,673)	[1]	(2,767)	[1]
Total shareholders' equity	21,089		21,431
BGE preference stock not subject to mandatory redemption	193		193
Noncontrolling interest	44		106
Total equity	21,326		21,730
Total liabilities and shareholders' equity	78,243		78,561
Member's equity
Accumulated other comprehensive income (loss), net	(2,673)	[1]	(2,767)	[1]
Noncontrolling interest	44		106
Removal Costs [Member]
Current liabilities
Regulatory liabilities	98		97
Deferred credits and other liabilities
Regulatory liabilities	1,417		1,406
Exelon Generation Co L L C [Member]
Current assets
Cash and cash equivalents	132		596
Cash and cash equivalents of variable interest entities	93		75
Restricted cash and cash equivalents	0		0
Restricted cash and investments of variable interest entity	13		16
Accounts receivable, net
Customer	1,470		1,482
Other	286		472
Accounts receivable of variable interest entities	285		292
Mark-to-market derivative assets	666		938
Mark-to-market derivative assets with affiliates	85		226
Receivables from affiliates	132		141
Unamortized energy contracts assets	727		886
Inventories, net
Fossil fuel	92		130
Materials and supplies	635		626
Deferred income taxes	187
Other	459		331
Total current assets	5,262		6,211
Property, plant and equipment, net	19,813		19,531
Deferred debits and other assets
Nuclear decommissioning trust funds	7,559		7,248
Investments	411		420
Investments in affiliates	0		0
Investment in CENG	1,883		1,849
Mark-to-market derivative assets	694		924
Prepaid pension asset	2,032		1,975
Pledged assets for Zion Station decommissioning	580		614
Unamortized energy contracts assets	968		1,073
Other	789		836
Total deferred debits and other assets	14,916		14,939
Total assets	39,991		40,681
Current liabilities
Short-term borrowings	13		0
Long-term debt due within one year	523		24
Long-term debt of variable interest entities due within one year	5		4
Accounts payable	1,162		1,346
Accounts payable of variable interest entities	188		202
Accrued expenses	904		1,116
Payables to affiliates	165		193
Deferred income taxes	18		128
Mark-to-market derivative liabilities	166		334
Unamortized energy contract liabilities	349		378
Other	371		372
Total current liabilities	3,864		4,097
Long-term debt	4,893		5,245
Long-term debt to affiliate	1,997		2,007
Long-term debt of variable interest entity	203		203
Deferred credits and other liabilities
Deferred income taxes and unamortized investment tax credits	5,598		5,398
Asset retirement obligations	5,013		4,938
Non-pension postretirement benefit obligations	785		755
Spent nuclear fuel obligation	1,020		1,020
Payables to affiliates	2,531		2,397
Mark-to-market derivative liabilities	199		232
Unamortized energy contract liabilities	457		516
Payable for Zion Station decommissioning	372		432
Other	789		776
Total deferred credits and other liabilities	16,764		16,464
Total liabilities	27,721		28,016
Commitments and contingencies	0		0
Shareholders' equity
Accumulated other comprehensive income (loss), net	409	[1]	513	[1]
Noncontrolling interest	46		108
Member's equity
Membership interest	8,876		8,876
Undistributed earnings	2,939		3,168
Accumulated other comprehensive income (loss), net	409	[1]	513	[1]
Total member's equity	12,224		12,557
Noncontrolling interest	46		108
Total equity	12,270		12,665
Total liabilities and equity	39,991		40,681
Commonwealth Edison Co [Member]
Current assets
Cash and cash equivalents	30		144
Restricted cash and cash equivalents	0		0
Accounts receivable, net
Customer	495		539
Other	513		452
Inventories, net
Inventories, net	100		91
Deferred income taxes	37		83
Counterparty collateral deposited	36		53
Regulatory assets	301		388
Other	26		25
Total current assets	1,538		1,775
Property, plant and equipment, net	14,020		13,826
Deferred debits and other assets
Regulatory assets	681		666
Investments	7		8
Investments in affiliates	6		6
Goodwill	2,625		2,625
Receivable from affiliate	2,314		2,039
Prepaid pension asset	1,729		1,661
Other	336		299
Total deferred debits and other assets	7,698		7,304
Total assets	23,256		22,905
Current liabilities
Short-term borrowings	220		0
Long-term debt due within one year	869		252
Accounts payable	384		379
Accrued expenses	199		295
Payables to affiliates	68		97
Customer deposits	136		136
Regulatory liabilities	166		170
Mark-to-market derivative liabilities	15		18
Mark-to-market derivative liabilities with affiliate	85		226
Other	94		82
Total current liabilities	2,236		1,655
Long-term debt	4,699		5,315
Long-term debt of variable financing trusts	206		206
Deferred credits and other liabilities
Deferred income taxes and unamortized investment tax credits	3,933		4,272
Asset retirement obligations	100		99
Non-pension postretirement benefit obligations	300		273
Regulatory liabilities	3,337		3,229
Mark-to-market derivative liabilities	60		49
Other	1,026		484
Total deferred credits and other liabilities	8,756		8,406
Total liabilities	15,897		15,582
Commitments and contingencies	0		0
Shareholders' equity
Common stock	1,588		1,588
Other paid-in capital	5,186		5,014
Retained earnings	585		721
Accumulated other comprehensive income (loss), net	0		0
Total shareholders' equity	7,359		7,323
Total liabilities and shareholders' equity	23,256		22,905
Member's equity
Accumulated other comprehensive income (loss), net	0		0
Commonwealth Edison Co [Member] | Removal Costs [Member]
Current liabilities
Regulatory liabilities	77		75
Deferred credits and other liabilities
Regulatory liabilities	1,199		1,192
PECO Energy Co [Member]
Current assets
Cash and cash equivalents	302		362
Restricted cash and cash equivalents	0		0
Accounts receivable, net
Customer	395		364
Other	138		161
Inventories, net
Fossil fuel	18		65
Materials and supplies	20		19
Deferred income taxes	40		40
Receivable from Exelon intercompany money pool	50		0
Prepaid utility taxes	96		21
Regulatory assets	33		32
Other	32		30
Total current assets	1,124		1,094
Property, plant and equipment, net	6,141		6,078
Deferred debits and other assets
Regulatory assets	1,389		1,378
Investments	23		22
Investments in affiliates	8		8
Receivable from affiliate	392		360
Prepaid pension asset	378		373
Other	36		40
Total deferred debits and other assets	2,226		2,181
Total assets	9,491		9,353
Current liabilities
Short-term notes payable - accounts receivable agreement	210		210
Long-term debt due within one year	300		300
Accounts payable	224		244
Accrued expenses	97		82
Payables to affiliates	76		76
Customer deposits	49		51
Regulatory liabilities	205		169
Other	28		26
Total current liabilities	1,189		1,158
Long-term debt	1,648		1,647
Long-term debt of variable financing trusts	184		184
Deferred credits and other liabilities
Deferred income taxes and unamortized investment tax credits	2,374		2,331
Asset retirement obligations	29		29
Non-pension postretirement benefit obligations	289		284
Regulatory liabilities	560		538
Other	111		113
Total deferred credits and other liabilities	3,363		3,295
Total liabilities	6,384		6,284
Commitments and contingencies	0		0
Preferred securities	87		87
Shareholders' equity
Common stock	2,388		2,388
Retained earnings	631		593
Accumulated other comprehensive income (loss), net	1	[1]	1	[1]
Total shareholders' equity	3,020		2,982
Total liabilities and shareholders' equity	9,491		9,353
Member's equity
Accumulated other comprehensive income (loss), net	1	[1]	1	[1]
PECO Energy Co [Member] | Removal Costs [Member]
Current liabilities
Regulatory liabilities	0		0
Deferred credits and other liabilities
Regulatory liabilities	0		0
Baltimore Gas and Electric Company [Member]
Current assets
Cash and cash equivalents	115		89
Restricted cash and cash equivalents	3
Restricted cash and investments of variable interest entity	52		30
Accounts receivable, net
Customer	476		403
Other	135		117
Income taxes receivable	39		3
Inventories, net
Fossil fuel	12		51
Materials and supplies	35		31
Deferred income taxes	7		1
Prepaid utility taxes	28		57
Regulatory assets	148		190
Other	8		8
Total current assets	1,058		980
Property, plant and equipment, net	5,568		5,498
Deferred debits and other assets
Regulatory assets	522		522
Investments	5		5
Investments in affiliates	8		8
Prepaid pension asset	456		467
Other	22		26
Total deferred debits and other assets	1,013		1,028
Total assets	7,639		7,506
Current liabilities
Long-term debt due within one year	400		400
Long-term debt of variable interest entities due within one year	67		67
Accounts payable	186		195
Accrued expenses	100		106
Payables to affiliates	45		65
Deferred income taxes	0		0
Customer deposits	69		71
Regulatory liabilities	47		29
Other	45		47
Total current liabilities	959		980
Long-term debt	1,446		1,446
Long-term debt of variable financing trusts	258		258
Long-term debt of variable interest entity	265		265
Deferred credits and other liabilities
Deferred income taxes and unamortized investment tax credits	1,738		1,658
Asset retirement obligations	7		8
Non-pension postretirement benefit obligations	227		229
Regulatory liabilities	218		214
Other	86		90
Total deferred credits and other liabilities	2,276		2,199
Total liabilities	5,204		5,148
Commitments and contingencies	0		0
Shareholders' equity
Common stock	1,360		1,360
Retained earnings	885		808
Total shareholders' equity	2,245		2,168
BGE preference stock not subject to mandatory redemption	190		190
Total equity	2,435		2,358
Total liabilities and shareholders' equity	7,639		7,506
Baltimore Gas and Electric Company [Member] | Removal Costs [Member]
Current liabilities
Regulatory liabilities	21		22
Deferred credits and other liabilities
Regulatory liabilities	$ 218		$ 214

[1] (a) All amounts are net of tax. Amounts in parenthesis represent a decrease in accumulated other comprehensive income.