Consolidated Statements of Cash Flows (Unaudited) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Cash flows from operating activities
Net income	$ 1	$ 200
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation, amortization and accretion	1,017	776
Impairment of assets held for sale	0	0
Deferred income taxes and amortization of investment tax credits	(610)	101
Net fair value changes related to derivatives	388	(73)
Net realized and unrealized (gains) losses on nuclear decommissioning trust fund investments	(66)	(103)
Other non-cash operating activities	231	530
Changes in assets and liabilities:
Accounts receivable	(70)	394
Inventories	101	104
Accounts payable, accrued expenses and other current liabilities	(542)	(1,176)
Option premiums paid, net	(3)	(100)
Counterparty collateral (posted) received, net	(186)	340
Income taxes	632	178
Pension and non-pension postretirement benefit contributions	(267)	(55)
Other assets and liabilities	233	(122)
Net cash flows provided by operating activities	859	994
Cash flows from investing activities
Capital expenditures	(1,447)	(1,496)
Proceeds from nuclear decommissioning trust fund sales	677	3,680
Investment in nuclear decommissioning trust funds	(729)	(3,726)
Cash acquired from Constellation	0	964
Acquisitions		0
Proceeds from sales of investments	0	0
Purchases of investments	0	0
Change in restricted cash	(12)	(8)
Other investing activities	40	(54)
Net cash flows provided by (used in) investing activities	(1,471)	(640)
Cash flows from financing activities
Changes in short-term debt	233	141
Issuance of long-term debt	149	0
Retirement or repayment of long-term debt	(1)	(451)
Dividends paid on common stock	(450)	(350)
Dividends paid to former Constellation shareholders	0	0
Proceeds from employee stock plans	12	12
Other financing activities	(45)	(1)
Net cash flows used in financing activities	(102)	(649)
Increase (decrease) in cash and cash equivalents	(714)	(295)
Cash and cash equivalents at beginning of period	1,486	1,016
Cash and cash equivalents at end of period	772	721
Exelon Generation Co L L C [Member]
Cash flows from operating activities
Net income	(17)	166
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation, amortization and accretion	688	547
Impairment of assets held for sale	0
Deferred income taxes and amortization of investment tax credits	(81)	165
Net fair value changes related to derivatives	406	(63)
Net realized and unrealized (gains) losses on nuclear decommissioning trust fund investments	(66)	(103)
Other non-cash operating activities	66	90
Changes in assets and liabilities:
Accounts receivable	65	321
Receivables from and payables to affiliates, net	(23)	85
Inventories	29	59
Accounts payable, accrued expenses and other current liabilities	(261)	(782)
Option premiums paid, net	(3)	(100)
Counterparty collateral (posted) received, net	(203)	348
Income taxes	180	162
Pension and non-pension postretirement benefit contributions	(115)	(20)
Other assets and liabilities	(159)	(80)
Net cash flows provided by operating activities	506	795
Cash flows from investing activities
Capital expenditures	(841)	(1,055)
Proceeds from nuclear decommissioning trust fund sales	677	3,680
Investment in nuclear decommissioning trust funds	(729)	(3,726)
Cash acquired from Constellation	0	708
Acquisitions		0
Change in restricted cash	3	(1)
Other investing activities	25	(77)
Net cash flows provided by (used in) investing activities	(865)	(471)
Cash flows from financing activities
Changes in short-term debt	13	0
Issuance of long-term debt	149	0
Retirement or repayment of long-term debt	(1)	(1)
Distribution to member	(211)	(600)
Contributions from member	0	0
Other financing activities	(37)	0
Net cash flows used in financing activities	(87)	(601)
Increase (decrease) in cash and cash equivalents	(446)	(277)
Cash and cash equivalents at beginning of period	671	496
Cash and cash equivalents at end of period	225	219
Commonwealth Edison Co [Member]
Cash flows from operating activities
Net income	(81)	87
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation, amortization and accretion	167	149
Deferred income taxes and amortization of investment tax credits	(295)	57
Other non-cash operating activities	42	60
Changes in assets and liabilities:
Accounts receivable	1	58
Receivables from and payables to affiliates, net	(32)	15
Inventories	(9)	(3)
Accounts payable, accrued expenses and other current liabilities	(73)	(159)
Counterparty collateral (posted) received, net	17	(8)
Income taxes	208	116
Pension and non-pension postretirement benefit contributions	(118)	(9)
Other assets and liabilities	231	(72)
Net cash flows provided by operating activities	58	291
Cash flows from investing activities
Capital expenditures	(346)	(291)
Proceeds from sales of investments	2	10
Purchases of investments	(1)	(5)
Change in restricted cash	0	0
Other investing activities	9	6
Net cash flows provided by (used in) investing activities	(336)	(280)
Cash flows from financing activities
Changes in short-term debt	220	302
Issuance of long-term debt	0	0
Retirement or repayment of long-term debt	0	(450)
Contributions from parent	0	0
Dividends paid on common stock	(55)	(75)
Other financing activities	(1)	(3)
Net cash flows used in financing activities	164	(226)
Increase (decrease) in cash and cash equivalents	(114)	(215)
Cash and cash equivalents at beginning of period	144	234
Cash and cash equivalents at end of period	30	19
PECO Energy Co [Member]
Cash flows from operating activities
Net income	122	97
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation, amortization and accretion	57	53
Deferred income taxes and amortization of investment tax credits	19	10
Other non-cash operating activities	39	40
Changes in assets and liabilities:
Accounts receivable	(50)	31
Receivables from and payables to affiliates, net	1	12
Inventories	44	39
Accounts payable, accrued expenses and other current liabilities	(17)	(71)
Income taxes	29	76
Pension and non-pension postretirement benefit contributions	(11)	(5)
Other assets and liabilities	(38)	(110)
Net cash flows provided by operating activities	195	172
Cash flows from investing activities
Capital expenditures	(122)	(96)
Changes in intercompany money pool	(50)	(35)
Change in restricted cash	0	(3)
Other investing activities	1	4
Net cash flows provided by (used in) investing activities	(171)	(130)
Cash flows from financing activities
Changes in short-term debt	0	0
Issuance of long-term debt	0	0
Contributions from parent	0	0
Dividends paid on common stock	(83)	(87)
Dividends paid on preferred securities	(1)	(1)
Other financing activities	0	0
Net cash flows used in financing activities	(84)	(88)
Increase (decrease) in cash and cash equivalents	(60)	(46)
Cash and cash equivalents at beginning of period	362	194
Cash and cash equivalents at end of period	302	148
Baltimore Gas and Electric Company [Member]
Cash flows from operating activities
Net income	80	(30)
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation, amortization and accretion	93	79
Deferred income taxes and amortization of investment tax credits	73	40
Other non-cash operating activities	42	179
Changes in assets and liabilities:
Accounts receivable	(98)	6
Receivables from and payables to affiliates, net	(22)	31
Inventories	35	50
Accounts payable, accrued expenses and other current liabilities	(11)	(22)
Income taxes	(36)	(57)
Pension and non-pension postretirement benefit contributions	(5)	(7)
Other assets and liabilities	34	(11)
Net cash flows provided by operating activities	185	258
Cash flows from investing activities
Capital expenditures	(134)	(130)
Change in restricted cash	(22)	(19)
Other investing activities	2	3
Net cash flows provided by (used in) investing activities	(154)	(146)
Cash flows from financing activities
Changes in short-term debt		0
Issuance of long-term debt	0
Retirement or repayment of long-term debt	0	0
Contributions from parent	0
Dividends paid on common stock	0	0
Dividends paid on preferred securities	(3)	(3)
Change in restricted cash for dividends	(3)
Other financing activities	1	(1)
Net cash flows used in financing activities	(5)	(4)
Increase (decrease) in cash and cash equivalents	26	108
Cash and cash equivalents at beginning of period	89	49
Cash and cash equivalents at end of period	$ 115	$ 157