Consolidated Statements of Cash Flows (Unaudited) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Cash flows from operating activities
Net income	$ 1,171.00	$ 2,499.00	$ 2,563.00
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation, amortization and accretion	4,079.00	2,316.00	2,943.00
Impairment of assets held for sale	272.00	0	0
Deferred income taxes and amortization of investment tax credits	615.00	1,457.00	981.00
Net fair value changes related to derivatives	(604.00)	291.00	(88.00)
Net realized and unrealized (gains) losses on nuclear decommissioning trust fund investments	(157.00)	14.00	(105.00)
Other non-cash operating activities	1,383.00	770.00	609.00
Changes in assets and liabilities:
Accounts receivable	243.00	57.00	(232.00)
Inventories	26.00	(58.00)	(62.00)
Accounts payable, accrued expenses and other current liabilities	(632.00)	(254.00)	472.00
Option premiums paid, net	(114.00)	(3.00)	(124.00)
Counterparty collateral (posted) received, net	135.00	(344.00)	(155.00)
Income taxes	544.00	492.00	(543.00)
Pension and non-pension postretirement benefit contributions	(462.00)	(2,360.00)	(959.00)
Other assets and liabilities	(368.00)	(24.00)	(56.00)
Net cash flows provided by operating activities	6,131.00	4,853.00	5,244.00
Cash flows from investing activities
Capital expenditures	(5,789.00)	(4,042.00)	(3,326.00)
Proceeds from nuclear decommissioning trust fund sales	7,265.00	6,139.00	3,764.00
Investment in nuclear decommissioning trust funds	(7,483.00)	(6,332.00)	(3,907.00)
Cash acquired from Constellation	964.00
Proceeds from sale of Three Maryland Generating Stations	371.00
Acquisitions	(21.00)	(387.00)	(893.00)
Proceeds from sales of investments	28.00	6.00	28.00
Purchases of investments	(13.00)	(4.00)	(22.00)
Change in restricted cash	(34.00)	(3.00)	423.00
Other investing activities	136.00	20.00	39.00
Net cash flows provided by (used in) investing activities	(4,576.00)	(4,603.00)	(3,894.00)
Cash flows from financing activities
Payment of accounts receivable agreement	(15.00)
Changes in short-term debt	(197.00)	161.00	(155.00)
Issuance of long-term debt	2,027.00	1,199.00	1,398.00
Retirement or repayment of long-term debt	(1,145.00)	(789.00)	(828.00)
Retirement of long-term debt of variable interest entity	0	0	(806.00)
Retirement of long-term debt to financing affiliates	0	0	0
Dividends paid on common stock	(1,716.00)	(1,393.00)	(1,389.00)
Proceeds from employee stock plans	72.00	38.00	48.00
Purchase of treasury stock	0	0	0
Purchase of forward contract in relation to certain treasury stock	0	0	0
Other financing activities	(111.00)	(62.00)	(16.00)
Net cash flows used in financing activities	(1,085.00)	(846.00)	(1,748.00)
Increase (decrease) in cash and cash equivalents	470.00	(596.00)	(398.00)
Cash and cash equivalents at beginning of period	1,016.00	1,612.00	2,010.00
Cash and cash equivalents at end of period	1,486.00	1,016.00	1,612.00
Exelon Generation Co L L C [Member]
Cash flows from operating activities
Net income	558.00	1,771.00	1,972.00
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation, amortization and accretion	2,966.00	1,539.00	1,341.00
Impairment of assets held for sale	272.00	0	0
Deferred income taxes and amortization of investment tax credits	408.00	551.00	741.00
Net fair value changes related to derivatives	(611.00)	291.00	(88.00)
Net realized and unrealized (gains) losses on nuclear decommissioning trust fund investments	(157.00)	14.00	(105.00)
Other non-cash operating activities	537.00	421.00	182.00
Changes in assets and liabilities:
Accounts receivable	248.00	(122.00)	0
Receivables from and payables to affiliates, net	39.00	208.00	(5.00)
Inventories	31.00	(47.00)	(70.00)
Accounts payable, accrued expenses and other current liabilities	(499.00)	34.00	(18.00)
Option premiums paid, net	(114.00)	(3.00)	(124.00)
Counterparty collateral (posted) received, net	95.00	(410.00)	(1.00)
Income taxes	114.00	193.00	(303.00)
Pension and non-pension postretirement benefit contributions	(178.00)	(1,070.00)	(445.00)
Other assets and liabilities	(128.00)	(57.00)	(45.00)
Net cash flows provided by operating activities	3,581.00	3,313.00	3,032.00
Cash flows from investing activities
Capital expenditures	(3,554.00)	(2,491.00)	(1,883.00)
Proceeds from nuclear decommissioning trust fund sales	7,265.00	6,139.00	3,764.00
Investment in nuclear decommissioning trust funds	(7,483.00)	(6,332.00)	(3,907.00)
Cash acquired from Constellation	708.00
Proceeds from sale of Three Maryland Generating Stations	371.00
Acquisitions	(21.00)	(387.00)	(893.00)
Change in restricted cash	4.00	0	4.00
Other investing activities	81.00	(6.00)	19.00
Net cash flows provided by (used in) investing activities	(2,629.00)	(3,077.00)	(2,896.00)
Cash flows from financing activities
Changes in short-term debt	(52.00)
Issuance of long-term debt	1,076.00	0	898.00
Retirement or repayment of long-term debt	(145.00)	(2.00)	(215.00)
Distribution to member	(1,626.00)	(172.00)	(1,508.00)
Contributions from member	48.00	30.00	62.00
Other financing activities	(78.00)	(52.00)	(16.00)
Net cash flows used in financing activities	(777.00)	(196.00)	(779.00)
Increase (decrease) in cash and cash equivalents	175.00	40.00	(643.00)
Cash and cash equivalents at beginning of period	496.00	456.00	1,099.00
Cash and cash equivalents at end of period	671.00	496.00	456.00
Commonwealth Edison Co [Member]
Cash flows from operating activities
Net income	379.00	416.00	337.00
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation, amortization and accretion	610.00	554.00	517.00
Deferred income taxes and amortization of investment tax credits	270.00	700.00	582.00
Other non-cash operating activities	252.00	184.00	238.00
Changes in assets and liabilities:
Accounts receivable	24.00	5.00	(46.00)
Receivables from and payables to affiliates, net	(18.00)	(287.00)	(55.00)
Inventories	(11.00)	(9.00)	(1.00)
Accounts payable, accrued expenses and other current liabilities	59.00	(84.00)	342.00
Counterparty collateral (posted) received, net	40.00	66.00	(154.00)
Income taxes	9.00	223.00	(233.00)
Pension and non-pension postretirement benefit contributions	(138.00)	(977.00)	(317.00)
Other assets and liabilities	(142.00)	45.00	(133.00)
Net cash flows provided by operating activities	1,334.00	836.00	1,077.00
Cash flows from investing activities
Capital expenditures	(1,246.00)	(1,028.00)	(962.00)
Proceeds from sales of investments	28.00	6.00	28.00
Purchases of investments	(13.00)	(4.00)	(22.00)
Other investing activities	19.00	19.00	17.00
Net cash flows provided by (used in) investing activities	(1,212.00)	(1,007.00)	(939.00)
Cash flows from financing activities
Changes in short-term debt	0	0	(155.00)
Issuance of long-term debt	350.00	1,199.00	500.00
Retirement or repayment of long-term debt	(450.00)	(537.00)	(213.00)
Contributions from parent	0	0	2.00
Dividends paid on common stock	(105.00)	(300.00)	(310.00)
Other financing activities	(7.00)	(7.00)	(3.00)
Net cash flows used in financing activities	(212.00)	355.00	(179.00)
Increase (decrease) in cash and cash equivalents	(90.00)	184.00	(41.00)
Cash and cash equivalents at beginning of period	234.00	50.00	91.00
Cash and cash equivalents at end of period	144.00	234.00	50.00
PECO Energy Co [Member]
Cash flows from operating activities
Net income	381.00	389.00	324.00
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation, amortization and accretion	217.00	202.00	1,060.00
Deferred income taxes and amortization of investment tax credits	37.00	253.00	(400.00)
Other non-cash operating activities	125.00	100.00	108.00
Changes in assets and liabilities:
Accounts receivable	(14.00)	225.00	(212.00)
Receivables from and payables to affiliates, net	13.00	(217.00)	86.00
Inventories	21.00	0	9.00
Accounts payable, accrued expenses and other current liabilities	(47.00)	34.00	85.00
Income taxes	174.00	(45.00)	118.00
Pension and non-pension postretirement benefit contributions	(45.00)	(137.00)	(106.00)
Other assets and liabilities	16.00	14.00	78.00
Net cash flows provided by operating activities	878.00	818.00	1,150.00
Cash flows from investing activities
Capital expenditures	(422.00)	(481.00)	(545.00)
Changes in intercompany money pool	82.00	(82.00)	0
Change in restricted cash	2.00	(2.00)	414.00
Other investing activities	10.00	8.00	11.00
Net cash flows provided by (used in) investing activities	(328.00)	(557.00)	(120.00)
Cash flows from financing activities
Changes in short-term debt	(15.00)	0	0
Issuance of long-term debt	350.00	0	0
Retirement or repayment of long-term debt	(375.00)	(250.00)	0
Retirement of long-term debt of variable interest entity	0	0	(806.00)
Retirement of long-term debt to financing affiliates	0	0	0
Contributions from parent	9.00	18.00	43.00
Dividends paid on common stock	(343.00)	(348.00)	(224.00)
Dividends paid on preferred securities	(4.00)	(4.00)	(4.00)
Repayment of receivable from parent	0	0	180.00
Other financing activities	(4.00)	(5.00)	0
Net cash flows used in financing activities	(382.00)	(589.00)	(811.00)
Increase (decrease) in cash and cash equivalents	168.00	(328.00)	219.00
Cash and cash equivalents at beginning of period	194.00	522.00	303.00
Cash and cash equivalents at end of period	362.00	194.00	522.00
Baltimore Gas and Electric Company [Member]
Cash flows from operating activities
Net income	4.00	136.00	147.00
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation, amortization and accretion	298.00	274.00	249.00
Deferred income taxes and amortization of investment tax credits	104.00	145.00	299.00
Other non-cash operating activities	193.00	129.00	144.00
Changes in assets and liabilities:
Accounts receivable	(45.00)	60.00	(95.00)
Receivables from and payables to affiliates, net	26.00	(44.00)	(24.00)
Inventories	25.00	(10.00)	8.00
Accounts payable, accrued expenses and other current liabilities	(33.00)	(21.00)	(66.00)
Income taxes	14.00	35.00	(56.00)
Pension and non-pension postretirement benefit contributions	(16.00)	(67.00)	(214.00)
Other assets and liabilities	(85.00)	(161.00)	(63.00)
Net cash flows provided by operating activities	485.00	476.00	329.00
Cash flows from investing activities
Capital expenditures	(582.00)	(592.00)	(508.00)
Changes in intercompany money pool			315.00
Proceeds from sales of investments	0	0	21.00
Change in restricted cash	0	0	(5.00)
Other investing activities	9.00	0	0
Net cash flows provided by (used in) investing activities	(573.00)	(592.00)	(177.00)
Cash flows from financing activities
Changes in short-term debt	0	0	(46.00)
Issuance of long-term debt	250.00	300.00	0
Retirement or repayment of long-term debt	(173.00)	(82.00)	(57.00)
Contributions from parent	66.00	0	0
Dividends paid on common stock	0	(85.00)	0
Dividends paid on preferred securities	(13.00)	(13.00)	(13.00)
Other financing activities	(2.00)	(5.00)	0
Net cash flows used in financing activities	128.00	115.00	(116.00)
Increase (decrease) in cash and cash equivalents	40.00	(1.00)	36.00
Cash and cash equivalents at beginning of period	49.00	50.00	14.00
Cash and cash equivalents at end of period	$ 89.00	$ 49.00	$ 50.00