Consolidated Statements of Cash Flows (Unaudited) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Net Cash Provided by (Used in) Operating Activities [Abstract]
Net income	$ 738us-gaap_ProfitLoss	$ 93us-gaap_ProfitLoss
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation, amortization, depletion and accretion, including nuclear fuel and energy contract amortization	948	908
Impairment of long-lived assets	0	1
Gain on sales of assets	(1)	(5)
Deferred income taxes and amortization of investment tax credits	129	(48)
Net fair value changes related to derivatives	(91)us-gaap_UnrealizedGainLossOnDerivatives	730us-gaap_UnrealizedGainLossOnDerivatives
Net realized and unrealized gains on nuclear decommissioning trust fund investments	(47)us-gaap_GainLossOnInvestments	(26)us-gaap_GainLossOnInvestments
Other non-cash operating activities	344us-gaap_OtherNoncashIncomeExpense	276us-gaap_OtherNoncashIncomeExpense
Changes in assets and liabilities:
Accounts receivable	(270)us-gaap_IncreaseDecreaseInReceivables	(606)us-gaap_IncreaseDecreaseInReceivables
Inventories	291us-gaap_IncreaseDecreaseInInventories	80us-gaap_IncreaseDecreaseInInventories
Accounts payable, accrued expenses and other current liabilities	(607)	157
Option premiums received, net	5	15
Counterparty collateral received (posted), net	31	(677)
Income taxes	174	17
Pension and non-pension postretirement benefit contributions	(269)	(472)
Other assets and liabilities	115	(278)
Net cash flows provided by operating activities	1,490	165
Cash flows from investing activities
Capital expenditures	(1,784)	(1,217)
Proceeds from nuclear decommissioning trust fund sales	1,681	1,825
Investment in nuclear decommissioning trust funds	(1,747)	(1,878)
Acquisition of businesses	(15)	0
Proceeds from sale of long-lived assets	142	18
Proceeds from termination of direct financing lease investment	0exc_ProceedsFromLeaseTermination	335exc_ProceedsFromLeaseTermination
Change in restricted cash	(26)	(40)
Other investing activities	(2)	(54)
Net cash flows used in investing activities	(1,751)	(1,011)
Net Cash Provided by (Used in) Financing Activities [Abstract]
Changes in short-term borrowings	(141)	638
Issuance of long-term debt	1,206	950
Retirement of long-term debt	(580)us-gaap_RepaymentsOfLongTermDebt	(1,150)us-gaap_RepaymentsOfLongTermDebt
Dividends paid on common stock	(269)us-gaap_PaymentsOfDividendsCommonStock	(266)us-gaap_PaymentsOfDividendsCommonStock
Proceeds from employee stock plans	8us-gaap_ProceedsFromStockPlans	7us-gaap_ProceedsFromStockPlans
Other financing activities	(16)	(28)
Net cash flows provided by financing activities	208	151
Decrease in cash and cash equivalents	(53)	(695)
Cash and cash equivalents at beginning of period	1,878	1,609
Cash and cash equivalents at end of period	1,825	914
Exelon Generation Co L L C [Member]
Net Cash Provided by (Used in) Operating Activities [Abstract]
Net income	485	(185)
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation, amortization, depletion and accretion, including nuclear fuel and energy contract amortization	591	557
Impairment of long-lived assets	0	1
Gain on sales of assets	1	(5)
Deferred income taxes and amortization of investment tax credits	89	(161)
Net fair value changes related to derivatives	(165)	737
Net realized and unrealized gains on nuclear decommissioning trust fund investments	(47)	(26)
Other non-cash operating activities	45	89
Changes in assets and liabilities:
Accounts receivable	24	(295)
Receivables from and payables to affiliates, net	(10)	3
Inventories	228	1
Accounts payable, accrued expenses and other current liabilities	(345)	128
Option premiums received, net	5	15
Counterparty collateral received (posted), net	62	(699)
Income taxes	(104)	(35)
Pension and non-pension postretirement benefit contributions	(107)	(191)
Other assets and liabilities	85	(103)
Net cash flows provided by operating activities	837	(169)
Cash flows from investing activities
Capital expenditures	(937)	(535)
Proceeds from nuclear decommissioning trust fund sales	1,681	1,825
Investment in nuclear decommissioning trust funds	(1,747)	(1,878)
Changes in intercompany money pool		44
Acquisition of businesses	(15)	0
Proceeds from sale of long-lived assets	142	18
Change in restricted cash	(21)	9
Other investing activities	(2)	(77)
Net cash flows used in investing activities	(899)	(594)
Changes in Exelon intercompany money pool	936
Net Cash Provided by (Used in) Financing Activities [Abstract]
Changes in short-term borrowings	(1)	354
Issuance of long-term debt	806	300
Retirement of long-term debt	(18)	(532)
Repayments of Related Party Debt	(550)	0
Other financing activities	(3)	(21)
Distribution to member	(1,356)	(30)
Changes in Exelon intercompany money pool	936
Net cash flows provided by financing activities	(186)	71
Decrease in cash and cash equivalents	(248)	(692)
Cash and cash equivalents at beginning of period	780	1,258
Cash and cash equivalents at end of period	532	566
Commonwealth Edison Co [Member]
Net Cash Provided by (Used in) Operating Activities [Abstract]
Net income	90	98
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation, amortization, depletion and accretion, including nuclear fuel and energy contract amortization	175	173
Deferred income taxes and amortization of investment tax credits	35	35
Other non-cash operating activities	126	36
Changes in assets and liabilities:
Accounts receivable	(38)	(64)
Receivables from and payables to affiliates, net	(2)	(19)
Inventories	(10)	2
Accounts payable, accrued expenses and other current liabilities	(126)	(57)
Income taxes	131	44
Pension and non-pension postretirement benefit contributions	(121)	(233)
Other assets and liabilities	(9)	(24)
Net cash flows provided by operating activities	251	(9)
Cash flows from investing activities
Capital expenditures	(530)	(341)
Proceeds from sales of investments	0	3
Other investing activities	7	8
Net cash flows used in investing activities	(523)	(330)
Net Cash Provided by (Used in) Financing Activities [Abstract]
Changes in short-term borrowings	(21)	350
Issuance of long-term debt	400	650
Retirement of long-term debt	0	(617)
Dividends paid on common stock	(75)	(76)
Other financing activities	(4)	(1)
Contributions from parent	14	38
Net cash flows provided by financing activities	314	344
Decrease in cash and cash equivalents	42	5
Cash and cash equivalents at beginning of period	66	36
Cash and cash equivalents at end of period	108	41
PECO Energy Co [Member]
Net Cash Provided by (Used in) Operating Activities [Abstract]
Net income	139	89
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation, amortization, depletion and accretion, including nuclear fuel and energy contract amortization	62	58
Gain on sales of assets		0
Deferred income taxes and amortization of investment tax credits	5	(2)
Other non-cash operating activities	44	49
Changes in assets and liabilities:
Accounts receivable	(115)	(110)
Receivables from and payables to affiliates, net	5	2
Inventories	34	45
Accounts payable, accrued expenses and other current liabilities	1	117
Income taxes	67	33
Pension and non-pension postretirement benefit contributions	(12)	(11)
Other assets and liabilities	(72)	(127)
Net cash flows provided by operating activities	158	143
Cash flows from investing activities
Capital expenditures	(148)	(184)
Other investing activities	4	2
Net cash flows used in investing activities	(144)	(182)
Changes in Exelon intercompany money pool	65
Net Cash Provided by (Used in) Financing Activities [Abstract]
Dividends paid on common stock	(70)	(80)
Other financing activities	(1)	0
Changes in Exelon intercompany money pool	65
Net cash flows provided by financing activities	(6)	(80)
Decrease in cash and cash equivalents	8	(119)
Cash and cash equivalents at beginning of period	30	217
Cash and cash equivalents at end of period	38	98
Baltimore Gas and Electric Company [Member]
Net Cash Provided by (Used in) Operating Activities [Abstract]
Net income	109	88
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation, amortization, depletion and accretion, including nuclear fuel and energy contract amortization	106	108
Deferred income taxes and amortization of investment tax credits	33	27
Other non-cash operating activities	64	43
Changes in assets and liabilities:
Accounts receivable	(141)	(132)
Receivables from and payables to affiliates, net	(8)	(8)
Inventories	38	33
Accounts payable, accrued expenses and other current liabilities	(8)	(16)
Counterparty collateral received (posted), net	(27)	22
Income taxes	26	31
Pension and non-pension postretirement benefit contributions	(4)	(5)
Other assets and liabilities	93	44
Net cash flows provided by operating activities	281	235
Cash flows from investing activities
Capital expenditures	(136)	(146)
Change in restricted cash	2	(47)
Other investing activities	2	6
Net cash flows used in investing activities	(132)	(187)
Net Cash Provided by (Used in) Financing Activities [Abstract]
Changes in short-term borrowings	(120)	(66)
Dividends paid on common stock	(36)	0
Other financing activities	(13)	13
Contributions from parent	0
Dividends paid on preferred securities	(3)	(3)
Net cash flows provided by financing activities	(172)	(56)
Decrease in cash and cash equivalents	(23)	(8)
Cash and cash equivalents at beginning of period	64
Cash and cash equivalents at end of period	$ 41	$ 23

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