Consolidated Statements of Cash Flows (Unaudited) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Cash flows from operating activities
Net income	$ 93	$ 1
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation, amortization and accretion	908	1,017
Impairment of assets held for sale	0
Deferred income taxes and amortization of investment tax credits	(48)	(610)
Net fair value changes related to derivatives	730	388
Net realized and unrealized (gains) losses on nuclear decommissioning trust fund investments	(26)	(66)
Other non-cash operating activities	272	231
Changes in assets and liabilities:
Accounts receivable	(606)	(70)
Inventories	80	101
Accounts payable, accrued expenses and other current liabilities	157	(542)
Option premiums paid, net	15	(3)
Counterparty collateral (posted) received, net	(677)	(186)
Income taxes	17	632
Pension and non-pension postretirement benefit contributions	(472)	(267)
Other assets and liabilities	(278)	233
Net cash flows provided by operating activities	165	859
Cash flows from investing activities
Capital expenditures	(1,217)	(1,447)
Proceeds from nuclear decommissioning trust fund sales	1,825	677
Investment in nuclear decommissioning trust funds	(1,878)	(729)
Proceeds from sale of long-lived assets	18
Cash acquired from Constellation	0
Proceeds from sales of investments	0
Purchases of investments	0
Change in restricted cash	(40)	(12)
Other investing activities	(54)	40
Net cash flows provided by (used in) investing activities	(1,011)	(1,471)
Cash flows from financing activities
Payment of accounts receivable agreement	0
Changes in short-term debt	638	233
Redemption of preferred securities	0
Issuance of long-term debt	950	149
Retirement or repayment of long-term debt	(1,150)	(1)
Dividends paid on common stock	(266)	(450)
Dividends paid to former Constellation shareholders	0
Proceeds from employee stock plans	7	12
Other financing activities	(28)	(45)
Net cash flows used in financing activities	151	(102)
Increase (decrease) in cash and cash equivalents	(695)	(714)
Cash and cash equivalents at beginning of period	1,609	1,486
Cash and cash equivalents at end of period	914	772
CityPublicServiceBoardSanAntonio [Member] | EquipmentLeasedToOtherPartyMember
Cash flows from investing activities
Cash Proceeds from Direct Finance Lease Contract Termination	335	0
Exelon Generation Co L L C [Member]
Cash flows from operating activities
Net income	(185)	(17)
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation, amortization and accretion	557	688
Impairment of assets held for sale	0	0
Deferred income taxes and amortization of investment tax credits	(161)	(81)
Net fair value changes related to derivatives	737	406
Net realized and unrealized (gains) losses on nuclear decommissioning trust fund investments	(26)	(66)
Other non-cash operating activities	85	66
Changes in assets and liabilities:
Accounts receivable	(295)	65
Receivables from and payables to affiliates, net	(3)	(23)
Inventories	1	29
Accounts payable, accrued expenses and other current liabilities	128	(261)
Option premiums paid, net	15	(3)
Counterparty collateral (posted) received, net	(699)	(203)
Income taxes	(35)	180
Pension and non-pension postretirement benefit contributions	(191)	(115)
Other assets and liabilities	(103)	(159)
Net cash flows provided by operating activities	(169)	506
Cash flows from investing activities
Capital expenditures	(535)	(841)
Changes in intercompany money pool	(44)
Proceeds from nuclear decommissioning trust fund sales	1,825	677
Investment in nuclear decommissioning trust funds	(1,878)	(729)
Proceeds from sale of long-lived assets	18
Change in restricted cash	9	3
Other investing activities	(77)	25
Net cash flows provided by (used in) investing activities	(594)	(865)
Cash flows from financing activities
Changes in short-term debt	354	13
Issuance of long-term debt	300	149
Retirement or repayment of long-term debt	(532)	(1)
Distribution to member	(30)	(211)
Contributions from member	0	0
Other financing activities	(21)	(37)
Net cash flows used in financing activities	71	(87)
Increase (decrease) in cash and cash equivalents	(692)	(446)
Cash and cash equivalents at beginning of period	1,258	671
Cash and cash equivalents at end of period	566	225
Exelon Generation Co L L C [Member] | CityPublicServiceBoardSanAntonio [Member] | EquipmentLeasedToOtherPartyMember
Cash flows from investing activities
Cash Proceeds from Direct Finance Lease Contract Termination	335
Commonwealth Edison Co [Member]
Cash flows from operating activities
Net income	98	(81)
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation, amortization and accretion	173	167
Deferred income taxes and amortization of investment tax credits	35	(295)
Other non-cash operating activities	36	42
Changes in assets and liabilities:
Accounts receivable	(64)	1
Receivables from and payables to affiliates, net	(19)	(32)
Inventories	2	(9)
Accounts payable, accrued expenses and other current liabilities	(57)	(73)
Income taxes	44	208
Pension and non-pension postretirement benefit contributions	(233)	(118)
Other assets and liabilities	(24)	248
Net cash flows provided by operating activities	(9)	58
Cash flows from investing activities
Capital expenditures	(341)	(346)
Proceeds from sales of investments	3	2
Purchases of investments	0	(1)
Change in restricted cash	0	0
Other investing activities	8	9
Net cash flows provided by (used in) investing activities	(330)	(336)
Cash flows from financing activities
Changes in short-term debt	350	220
Issuance of long-term debt	650	0
Retirement or repayment of long-term debt	(617)	0
Contributions from parent	38	0
Dividends paid on common stock	(76)	(55)
Other financing activities	(1)	(1)
Net cash flows used in financing activities	344	164
Increase (decrease) in cash and cash equivalents	5	(114)
Cash and cash equivalents at beginning of period	36	144
Cash and cash equivalents at end of period	41	30
PECO Energy Co [Member]
Cash flows from operating activities
Net income	89	122
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation, amortization and accretion	58	57
Deferred income taxes and amortization of investment tax credits	(2)	19
Other non-cash operating activities	49	39
Changes in assets and liabilities:
Accounts receivable	(110)	(50)
Receivables from and payables to affiliates, net	2	1
Inventories	45	44
Accounts payable, accrued expenses and other current liabilities	117	(17)
Income taxes	33	29
Pension and non-pension postretirement benefit contributions	(11)	(11)
Other assets and liabilities	(127)	(38)
Net cash flows provided by operating activities	143	195
Cash flows from investing activities
Capital expenditures	(184)	(122)
Changes in intercompany money pool	0	(50)
Change in restricted cash	0	0
Other investing activities	2	1
Net cash flows provided by (used in) investing activities	(182)	(171)
Cash flows from financing activities
Changes in short-term debt	0	0
Redemption of preferred securities	0
Issuance of long-term debt	0	0
Dividends paid on common stock	(80)	(83)
Dividends paid on preferred securities	0	(1)
Other financing activities	0	0
Net cash flows used in financing activities	(80)	(84)
Increase (decrease) in cash and cash equivalents	(119)	(60)
Cash and cash equivalents at beginning of period	217	362
Cash and cash equivalents at end of period	98	302
Baltimore Gas and Electric Company [Member]
Cash flows from operating activities
Net income	88	80
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation, amortization and accretion	108	93
Deferred income taxes and amortization of investment tax credits	27	73
Other non-cash operating activities	43	42
Changes in assets and liabilities:
Accounts receivable	(132)	(98)
Receivables from and payables to affiliates, net	(8)	(22)
Inventories	33	35
Accounts payable, accrued expenses and other current liabilities	(16)	(11)
Counterparty collateral (posted) received, net	22	0
Income taxes	31	(36)
Pension and non-pension postretirement benefit contributions	(5)	(5)
Other assets and liabilities	44	34
Net cash flows provided by operating activities	235	185
Cash flows from investing activities
Capital expenditures	(146)	(134)
Change in restricted cash	(47)	(22)
Other investing activities	6	2
Net cash flows provided by (used in) investing activities	(187)	(154)
Cash flows from financing activities
Changes in short-term debt	(66)	0
Issuance of long-term debt	0	0
Retirement or repayment of long-term debt	0	0
Contributions from parent	0	0
Dividends paid on common stock	0	0
Dividends paid on preferred securities	(3)	(3)
Change in restricted cash for dividends	0	(3)
Other financing activities	13	1
Net cash flows used in financing activities	(56)	(5)
Increase (decrease) in cash and cash equivalents	(8)	26
Cash and cash equivalents at beginning of period	31	89
Cash and cash equivalents at end of period	$ 23	$ 115