Consolidated Balance Sheets (Unaudited) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Current assets
Cash and cash equivalents	$ 1,411.00	$ 1,016.00
Cash and cash equivalents of variable interest entities	75.00
Restricted cash and investments	86.00	40.00
Restricted cash and investments of variable interest entity	47.00
Accounts receivable, net
Customer	2,787.00	1,613.00
Other	1,147.00	1,000.00
Accounts receivable of variable interest entities	292.00
Mark-to-market derivative assets	938.00	432.00
Unamortized energy contracts assets	886.00	16.00
Inventories, net
Fossil fuel	246.00	208.00
Materials and supplies	768.00	656.00
Deferred income taxes	131.00	0
Regulatory assets	759.00	390.00
Other	560.00	342.00
Total current assets	10,133.00	5,713.00
Property, plant and equipment, net	45,186.00	32,570.00
Deferred debits and other assets
Regulatory assets	6,497.00	4,518.00
Nuclear decommissioning trust funds	7,248.00	6,507.00
Investments	1,184.00	751.00
Investments in affiliates	22.00	15.00
Investment in CENG	1,849.00
Goodwill	2,625.00	2,625.00
Mark-to-market derivative assets	937.00	650.00
Pledged assets for Zion Station decommissioning	614.00	734.00
Unamortized energy contracts assets	1,073.00	424.00
Other	1,128.00	488.00
Deferred income taxes	58.00	0
Total deferred debits and other assets	23,235.00	16,712.00
Total assets	78,554.00	54,995.00
Current liabilities
Short-term borrowings	0	163.00
Short-term notes payable - accounts receivable agreement	210.00	225.00
Long-term debt due within one year	975.00	828.00
Long-term debt of variable interest entities due within one year	72.00
Accounts payable	2,446.00	1,444.00
Accounts payable of variable interest entities	202.00
Accrued expenses	1,800.00	1,255.00
Payables to affiliates	88.00	5.00
Deferred income taxes	58.00	1.00
Regulatory liabilities	321.00	197.00
Dividends payable	4.00	349.00
Mark-to-market derivative liabilities	352.00	112.00
Mark-to-market derivative liabilities with affiliate	0
Unamortized energy contract liabilities	455.00
Other	889.00	560.00
Total current liabilities	7,784.00	5,134.00
Long-term debt	17,190.00	11,799.00
Long-term debt of variable financing trusts	508.00	390.00
Long-term debt of variable interest entity	648.00
Deferred credits and other liabilities
Deferred income taxes and unamortized investment tax credits	11,551.00	8,253.00
Asset retirement obligations	5,074.00	3,884.00
Pension obligations	3,428.00	2,194.00
Non-pension postretirement benefit obligations	2,662.00	2,263.00
Spent nuclear fuel obligation	1,020.00	1,019.00
Regulatory liabilities	3,981.00	3,627.00
Mark-to-market derivative liabilities	281.00	126.00
Unamortized energy contract liabilities	528.00
Payable for Zion Station decommissioning	432.00	563.00
Other	1,650.00	1,268.00
Total deferred credits and other liabilities	30,607.00	23,197.00
Total liabilities	56,737.00	40,520.00
Commitments and contingencies	0	0
Preferred securities	87.00	87.00
Shareholders' equity
Common stock	16,632.00	9,107.00
Treasury stock, at cost (35 and 35 shares held at December 31, 2010 and December 31, 2009, respectively)	(2,327.00)	(2,327.00)
Retained earnings	9,893.00	10,055.00
Accumulated other comprehensive income (loss), net	(2,767.00)	(2,450.00)
Total shareholders' equity	21,431.00	14,385.00
BGE preference stock not subject to mandatory redemption	193.00
Noncontrolling interest	106.00	3.00
Total equity	21,730.00	14,388.00
Total liabilities and shareholders' equity	78,554.00	54,995.00
Member's equity
Accumulated other comprehensive income (loss), net	(2,767.00)	(2,450.00)
Noncontrolling interest	106.00	3.00
Removal Costs [Member]
Current liabilities
Regulatory liabilities	97.00	61.00
Deferred credits and other liabilities
Regulatory liabilities	1,406.00	1,185.00
Exelon Generation Co L L C [Member]
Current assets
Cash and cash equivalents	596.00	496.00
Cash and cash equivalents of variable interest entities	75.00
Restricted cash and cash equivalents	0	5.00
Restricted cash and investments of variable interest entity	16.00
Accounts receivable, net
Customer	1,482.00	578.00
Other	472.00	257.00
Accounts receivable of variable interest entities	292.00
Mark-to-market derivative assets	938.00	432.00
Mark-to-market derivative assets with affiliates	226.00	503.00
Receivables from affiliates	141.00	109.00
Unamortized energy contracts assets	886.00	16.00
Inventories, net
Fossil fuel	130.00	120.00
Materials and supplies	626.00	556.00
Other	331.00	145.00
Total current assets	6,211.00	3,217.00
Property, plant and equipment, net	19,531.00	13,475.00
Deferred debits and other assets
Nuclear decommissioning trust funds	7,248.00	6,507.00
Investments	420.00	42.00
Investment in CENG	1,849.00
Mark-to-market derivative assets	924.00	635.00
Mark-to-market derivative assets with affiliates	0	191.00
Prepaid pension asset	1,975.00	2,068.00
Pledged assets for Zion Station decommissioning	614.00	734.00
Unamortized energy contracts assets	1,073.00	424.00
Other	836.00	140.00
Total deferred debits and other assets	14,939.00	10,741.00
Total assets	40,681.00	27,433.00
Current liabilities
Short-term borrowings		2.00
Long-term debt due within one year	24.00	3.00
Long-term debt of variable interest entities due within one year	4.00
Accounts payable	1,346.00	753.00
Accounts payable of variable interest entities	202.00
Accrued expenses	1,116.00	779.00
Payables to affiliates	193.00	58.00
Deferred income taxes	128.00	244.00
Mark-to-market derivative liabilities	334.00	103.00
Mark-to-market derivative liabilities with affiliate	0
Unamortized energy contract liabilities	378.00
Other	372.00	202.00
Total current liabilities	4,097.00	2,144.00
Long-term debt	5,245.00	3,674.00
Long-term debt to affiliate	2,007.00
Long-term debt of variable interest entity	203.00
Deferred credits and other liabilities
Deferred income taxes and unamortized investment tax credits	5,398.00	3,966.00
Asset retirement obligations	4,938.00	3,767.00
Non-pension postretirement benefit obligations	755.00	703.00
Spent nuclear fuel obligation	1,020.00	1,019.00
Payables to affiliates	2,397.00	2,222.00
Mark-to-market derivative liabilities	232.00	29.00
Unamortized energy contract liabilities	516.00
Payable for Zion Station decommissioning	432.00	563.00
Other	776.00	638.00
Total deferred credits and other liabilities	16,464.00	12,907.00
Total liabilities	28,016.00	18,725.00
Commitments and contingencies	0	0
Shareholders' equity
Accumulated other comprehensive income (loss), net	513.00	915.00
Noncontrolling interest	108.00	5.00
Member's equity
Membership interest	8,876.00	3,556.00
Undistributed earnings	3,168.00	4,232.00
Accumulated other comprehensive income (loss), net	513.00	915.00
Total member's equity	12,557.00	8,703.00
Noncontrolling interest	108.00	5.00
Total equity	12,665.00	8,708.00
Total liabilities and equity	40,681.00	27,433.00
Commonwealth Edison Co [Member]
Current assets
Cash and cash equivalents	144.00	234.00
Restricted cash and cash equivalents	0	3.00
Accounts receivable, net
Customer	539.00	655.00
Other	452.00	385.00
Inventories, net
Inventories, net	91.00	81.00
Deferred income taxes	83.00	61.00
Counterparty collateral deposited	53.00	90.00
Regulatory assets	388.00	657.00
Other	25.00	22.00
Total current assets	1,775.00	2,188.00
Property, plant and equipment, net	13,826.00	13,121.00
Deferred debits and other assets
Regulatory assets	666.00	699.00
Investments	8.00	21.00
Investments in affiliates	6.00	6.00
Goodwill	2,625.00	2,625.00
Receivable from affiliate	2,039.00	1,860.00
Mark-to-market derivative assets	0	0
Prepaid pension asset	1,661.00	1,803.00
Other	299.00	315.00
Total deferred debits and other assets	7,304.00	7,329.00
Total assets	22,905.00	22,638.00
Current liabilities
Short-term borrowings	0	0
Long-term debt due within one year	252.00	450.00
Accounts payable	379.00	325.00
Accrued expenses	295.00	318.00
Payables to affiliates	97.00	111.00
Customer deposits	136.00	136.00
Regulatory liabilities	130.00	137.00
Mark-to-market derivative liabilities	18.00	9.00
Mark-to-market derivative liabilities with affiliate	226.00	503.00
Other	122.00	82.00
Total current liabilities	1,655.00	2,071.00
Long-term debt	5,315.00	5,215.00
Long-term debt of variable financing trusts	206.00	206.00
Deferred credits and other liabilities
Deferred income taxes and unamortized investment tax credits	4,272.00	3,993.00
Asset retirement obligations	99.00	89.00
Non-pension postretirement benefit obligations	273.00	271.00
Regulatory liabilities	3,229.00	3,042.00
Mark-to-market derivative liabilities	49.00	97.00
Mark-to-market derivative liabilities with affiliate	0	191.00
Other	484.00	426.00
Total deferred credits and other liabilities	8,406.00	8,109.00
Total liabilities	15,582.00	15,601.00
Commitments and contingencies	0	0
Shareholders' equity
Common stock	1,588.00	1,588.00
Other paid-in capital	5,014.00	5,003.00
Retained earnings	721.00	447.00
Accumulated other comprehensive income (loss), net	0	(1.00)
Total shareholders' equity	7,323.00	7,037.00
Total liabilities and shareholders' equity	22,905.00	22,638.00
Member's equity
Accumulated other comprehensive income (loss), net	0	(1.00)
Commonwealth Edison Co [Member] | Removal Costs [Member]
Current liabilities
Regulatory liabilities	75.00	61.00
Deferred credits and other liabilities
Regulatory liabilities	1,192.00	1,185.00
PECO Energy Co [Member]
Current assets
Cash and cash equivalents	362.00	194.00
Restricted cash and cash equivalents	0	2.00
Accounts receivable, net
Customer	364.00	380.00
Other	161.00	376.00
Inventories, net
Fossil fuel	65.00	87.00
Materials and supplies	19.00	18.00
Deferred income taxes	40.00	25.00
Receivable from Exelon intercompany money pool	0	82.00
Prepaid utility taxes	21.00	1.00
Regulatory assets	32.00	39.00
Other	30.00	39.00
Total current assets	1,094.00	1,243.00
Property, plant and equipment, net	6,078.00	5,874.00
Deferred debits and other assets
Regulatory assets	1,378.00	1,216.00
Investments	22.00	22.00
Investments in affiliates	8.00	8.00
Receivable from affiliate	360.00	365.00
Prepaid pension asset	373.00	382.00
Other	40.00	46.00
Total deferred debits and other assets	2,181.00	2,039.00
Total assets	9,353.00	9,156.00
Current liabilities
Short-term notes payable - accounts receivable agreement	210.00	225.00
Long-term debt due within one year	300.00	375.00
Long-term debt to PECO Energy Transition Trust due within one year	0	0
Accounts payable	244.00	262.00
Accrued expenses	82.00	83.00
Payables to affiliates	76.00	62.00
Deferred income taxes	0	0
Customer deposits	51.00	53.00
Regulatory liabilities	169.00	60.00
Mark-to-market derivative liabilities	0	0
Mark-to-market derivative liabilities with affiliate	0	0
Other	26.00	25.00
Total current liabilities	1,158.00	1,145.00
Long-term debt	1,647.00	1,597.00
Long-term debt of variable financing trusts	184.00	184.00
Deferred credits and other liabilities
Deferred income taxes and unamortized investment tax credits	2,331.00	2,170.00
Asset retirement obligations	29.00	28.00
Non-pension postretirement benefit obligations	284.00	288.00
Regulatory liabilities	538.00	585.00
Mark-to-market derivative liabilities	0	0
Mark-to-market derivative liabilities with affiliate	0	0
Other	113.00	134.00
Total deferred credits and other liabilities	3,295.00	3,205.00
Total liabilities	6,284.00	6,131.00
Preferred securities	87.00	87.00
Shareholders' equity
Common stock	2,388.00	2,379.00
Receivable from parent	0	0
Retained earnings	593.00	559.00
Accumulated other comprehensive income (loss), net	1.00	0
Total shareholders' equity	2,982.00	2,938.00
Total liabilities and shareholders' equity	9,353.00	9,156.00
Member's equity
Accumulated other comprehensive income (loss), net	1.00	0
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	89.00	49.00
Restricted cash and investments of variable interest entity	30.00	30.00
Accounts receivable, net
Customer	401.00	428.00
Other	117.00	90.00
Income taxes receivable	3.00	21.00
Inventories, net
Fossil fuel	51.00	74.00
Materials and supplies	31.00	34.00
Deferred income taxes	1.00
Prepaid utility taxes	57.00	56.00
Regulatory assets	185.00	175.00
Other	8.00	12.00
Total current assets	973.00	969.00
Property, plant and equipment, net	5,498.00	5,132.00
Deferred debits and other assets
Regulatory assets	522.00	551.00
Investments	5.00	0
Investments in affiliates	8.00	8.00
Prepaid pension asset	467.00	514.00
Other	26.00	29.00
Total deferred debits and other assets	1,028.00	1,102.00
Total assets	7,499.00	7,203.00
Current liabilities
Long-term debt due within one year	400.00	110.00
Long-term debt of variable interest entities due within one year	67.00	63.00
Accounts payable	195.00	210.00
Accrued expenses	106.00	110.00
Payables to affiliates	65.00	41.00
Deferred income taxes	0	59.00
Customer deposits	71.00	84.00
Regulatory liabilities	22.00	19.00
Other	47.00	38.00
Total current liabilities	973.00	734.00
Long-term debt	1,446.00	1,596.00
Long-term debt of variable financing trusts	258.00	258.00
Long-term debt of variable interest entity	265.00	332.00
Deferred credits and other liabilities
Deferred income taxes and unamortized investment tax credits	1,658.00	1,491.00
Asset retirement obligations	8.00	1.00
Non-pension postretirement benefit obligations	229.00	233.00
Regulatory liabilities	214.00	201.00
Other	90.00	56.00
Total deferred credits and other liabilities	2,199.00	1,982.00
Total liabilities	5,141.00	4,902.00
Shareholders' equity
Common stock	1,360.00	1,294.00
Retained earnings	808.00	817.00
Total shareholders' equity	2,168.00	2,111.00
BGE preference stock not subject to mandatory redemption	190.00	190.00
Total equity	2,358.00	2,301.00
Total liabilities and shareholders' equity	7,499.00	7,203.00
Baltimore Gas and Electric Company [Member] | Removal Costs [Member]
Current liabilities
Regulatory liabilities	22.00	18.00
Deferred credits and other liabilities
Regulatory liabilities	$ 214.00	$ 200.00