Supplemental Financial Information - Cash Flow (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment	$ 540		$ 481
Regulatory assets	58		72
Amortization of intangible assets, net	12		11
Amortization of energy contract assets and liabilities	(31)	[1]	42	[1]
Nuclear fuel	272	[2]	234	[2]
Asset retirement obligation accretion	97	[3]	68	[3]
Total depreciation, amortization and accretion	948		908
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefit Expense	159		173
Gain (loss) on equity method investments			19
Provision for uncollectible accounts	84		35
Stock-based compensation costs	39		46
Other Decommissioning Related Activity	(44)	[4]	(35)	[4]
Energy-related options	9	[5]	31	[5]
Amortization of regulatory asset related to debt costs			3
Amortization of rate stabilization deferral			20
Amortization of debt fair value adjustment	(9)		(12)
Discrete impacts from EIMA			(4)	[6]
Amortization of debt costs	18		5
Inventory Write-down	10		2
Other	4		(7)
Total other noncash operating activities	344		276
Changes In Other Assets and Liabilities [Abstract]
Under/over-recovered energy and transmission costs			(15)
Other regulatory assets and liabilities	92		(4)
Increase (Decrease) in Deposits	226	[7]
Increase (Decrease) in Other Current Liabilities	(155)
Increase (Decrease) in Other Noncurrent Assets and Liabilities, Net	113
Other current assets and liabilities			(209)
Other noncurrent assets and liabilities			(50)
Total changes in other assets and liabilities	115		(278)
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Total noncash investing and financing activities	0		0
Exelon Generation Co L L C [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment	242		200
Regulatory assets	0		0
Amortization of intangible assets, net	12		11
Amortization of energy contract assets and liabilities	(32)	[1]	44	[1]
Nuclear fuel	272	[2]	234	[2]
Asset retirement obligation accretion	97	[3]	68	[3]
Total depreciation, amortization and accretion	591		557
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefit Expense	67		75
Gain (loss) on equity method investments			19
Provision for uncollectible accounts	4		1
Stock-based compensation costs	0		0
Other Decommissioning Related Activity	(44)	[4]	(35)	[4]
Energy-related options	9	[5]	31	[5]
Amortization of regulatory asset related to debt costs	0		0
Amortization of rate stabilization deferral	0		0
Amortization of debt fair value adjustment	(4)		(5)
Discrete impacts from EIMA	0	[6]	0	[6]
Amortization of debt costs	4		3
Inventory Write-down	10		2
Other	(1)		(2)
Total other noncash operating activities	45		89
Changes In Other Assets and Liabilities [Abstract]
Under/over-recovered energy and transmission costs	0
Other regulatory assets and liabilities	0
Increase (Decrease) in Deposits	226	[7]
Increase (Decrease) in Other Current Liabilities	(100)
Increase (Decrease) in Other Noncurrent Assets and Liabilities, Net	41
Other current assets and liabilities			(80)
Other noncurrent assets and liabilities			(23)
Total changes in other assets and liabilities	85		(103)
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Total noncash investing and financing activities	0		0
Commonwealth Edison Co [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment	154		143
Regulatory assets	21		30
Total depreciation, amortization and accretion	175		173
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefit Expense	52		56
Provision for uncollectible accounts	22		(11)
Stock-based compensation costs	0
Energy-related options			0	[5]
Amortization of regulatory asset related to debt costs	2		2
Discrete impacts from EIMA	46	[6]	(4)	[6]
Amortization of debt costs	1		(5)
Inventory Write-down	0
Other	3		(2)
Total other noncash operating activities	126		36
Changes In Other Assets and Liabilities [Abstract]
Under/over-recovered energy and transmission costs	0		4
Other regulatory assets and liabilities	2		(10)
Increase (Decrease) in Deposits	0
Increase (Decrease) in Other Current Liabilities	(1)
Increase (Decrease) in Other Noncurrent Assets and Liabilities, Net	10
Other current assets and liabilities			(29)
Other noncurrent assets and liabilities			11
Total changes in other assets and liabilities	(9)		(24)
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Indemnification of like-kind exchange position	14		38
Total noncash investing and financing activities	2		2
Commonwealth Edison Co [Member] | Indemnification Agreement [Member]
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Indemnification of like-kind exchange position	2	[8]	2	[8]
PECO Energy Co [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment	58		56
Regulatory assets	4		2
Total depreciation, amortization and accretion	62		58
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefit Expense	10		12
Gain (loss) on equity method investments			0
Provision for uncollectible accounts	33		35
Stock-based compensation costs	0		0
Other Decommissioning Related Activity			0	[4]
Energy-related options			0	[5]
Amortization of regulatory asset related to debt costs	1		1
Amortization of rate stabilization deferral			0
Amortization of debt fair value adjustment			0
Discrete impacts from EIMA			0	[6]
Amortization of debt costs	1		1
Inventory Write-down	0
Other	(1)		0
Total other noncash operating activities	44		49
Changes In Other Assets and Liabilities [Abstract]
Under/over-recovered energy and transmission costs	26		(17)
Other regulatory assets and liabilities	(5)		(3)
Increase (Decrease) in Deposits	0
Increase (Decrease) in Other Current Liabilities	(95)	[9]
Increase (Decrease) in Other Noncurrent Assets and Liabilities, Net	(2)
Other current assets and liabilities			(105)	[9]
Other noncurrent assets and liabilities			(2)
Total changes in other assets and liabilities	(72)		(127)
Baltimore Gas and Electric Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment	71		70
Regulatory assets	35		38
Total depreciation, amortization and accretion	106		108
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefit Expense	16		16
Gain (loss) on equity method investments			0
Provision for uncollectible accounts	25		11
Stock-based compensation costs	0		0
Other Decommissioning Related Activity			0	[4]
Energy-related options			0	[5]
Amortization of regulatory asset related to debt costs	0		0
Amortization of rate stabilization deferral	25		20
Amortization of debt fair value adjustment			0
Discrete impacts from EIMA			0	[6]
Amortization of debt costs	1		0
Inventory Write-down	0
Other	(3)		(4)
Total other noncash operating activities	64		43
Changes In Other Assets and Liabilities [Abstract]
Under/over-recovered energy and transmission costs	39		23
Other regulatory assets and liabilities	25		6
Increase (Decrease) in Deposits	0
Increase (Decrease) in Other Current Liabilities	30
Increase (Decrease) in Other Noncurrent Assets and Liabilities, Net	1
Other current assets and liabilities			18
Other noncurrent assets and liabilities			(3)
Total changes in other assets and liabilities	93		44
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Indemnification of like-kind exchange position	$ 0

[1] Included in Operating revenues or Purchased power and fuel expense on the Registrants’ Consolidated Statements of Operations and Comprehensive Income.

[2] Included in Purchased power and fuel expense on the Registrants’ Consolidated Statements of Operations and Comprehensive Income.

[3] Included in Operating and maintenance expense on the Registrants’ Consolidated Statements of Operations and Comprehensive Income.

[4] Includes the elimination of NDT fund activity for the Regulatory Agreement Units, including the elimination of operating revenues, ARO accretion, ARC amortization, investment income and income taxes related to all NDT fund activity for these units. See Note 15 — Asset Retirement Obligations of the Exelon 2014 Form 10-K for additional information regarding the accounting for nuclear decommissioning.

[5] Includes option premiums reclassified to realized at the settlement of the underlying contracts and recorded to results of operations.

[6] Reflects the change in distribution rates pursuant to EIMA, which allows for the recovery of costs by a utility through a pre-established performance-based formula rate tariff. See Note 5 — Regulatory Matters for more information.

[7] Relates primarily to cash deposits recalled from ISOs/RTOs and replaced with letters of credit.

[8] See Note 10 — Income Taxes for discussion of the like-kind exchange tax position

[9] Relates primarily to prepaid utility taxes.