Supplemental Financial Information - Cash Flow (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014		Mar. 31, 2013
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment	$ 481		$ 471
Regulatory assets	72		61
Amortization of intangible assets, net	11		11
Amortization of energy contract assets and liabilities	42	[1]	176	[1]
Nuclear fuel	234	[1]	230	[1]
Asset retirement obligation accretion	68	[2]	68	[2]
Total depreciation, amortization and accretion	908		1,017
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefits costs	173		205
Provision for uncollectible accounts	35		45
Provision for Obsolete Inventory	2
Stock-based compensation costs	46		39
Other Decommissioning Related Activity	(35)	[3]	(64)	[3]
Energy-related options	31	[4]	21	[4]
Amortization of regulatory asset related to debt costs	3		4
Amortization of rate stabilization deferral	20		30
Amortization of debt fair value adjustment	(12)		(9)
Discrete impacts from EIMA	(4)		(49)	[5]
Merger related commitments			(6)
Gain (loss) on equity method investments	19		9
Amortization of debt costs	5		5
Other	(11)		1
Total other noncash operating activities	272		231
Changes In Other Assets and Liabilities [Abstract]
Under/over-recovered energy and transmission costs	(15)		29
Other regulatory assets and liabilities	4		(91)
Other current assets and liabilities	(209)		(169)
Other noncurrent assets and liabilities	(50)		282
Total changes in other assets and liabilities	(278)		233
Cash Flow Noncash Investing And Financing Activities Disclosure [Abstract]
Consolidated VIE dividend to non-controlling interest	(2)		63
Total noncash investing and financing activities	0		63
DOE Smart Grid Investment Grant [Abstract]
Amount included in capital expenditures	2		21
Smart Grid Grant Reimbursements	2		32
Exelon Generation Co L L C [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment	200		203
Amortization of intangible assets, net	11		11
Amortization of energy contract assets and liabilities	44	[1]	176	[1]
Nuclear fuel	234	[1]	230	[1]
Asset retirement obligation accretion	68	[2]	68	[2]
Total depreciation, amortization and accretion	557		688
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefits costs	75		87
Provision for uncollectible accounts	1		7
Provision for Obsolete Inventory	2
Stock-based compensation costs	0		4
Other Decommissioning Related Activity	(35)	[3]	(64)	[3]
Energy-related options	31	[4]	21	[4]
Amortization of debt fair value adjustment	(5)		(9)
Merger related commitments			0
Gain (loss) on equity method investments	19		9
Amortization of debt costs	3		3
Other	(6)		8
Total other noncash operating activities	85		66
Changes In Other Assets and Liabilities [Abstract]
Other current assets and liabilities	(80)		(131)
Other noncurrent assets and liabilities	(23)		(28)
Total changes in other assets and liabilities	(103)		(159)
Cash Flow Noncash Investing And Financing Activities Disclosure [Abstract]
Consolidated VIE dividend to non-controlling interest			63
Total noncash investing and financing activities	0		63
Commonwealth Edison Co [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment	143		137
Regulatory assets	30		30
Total depreciation, amortization and accretion	173		167
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefits costs	56		77
Provision for uncollectible accounts	(11)		9
Stock-based compensation costs	0		1
Amortization of regulatory asset related to debt costs	2		3
Discrete impacts from EIMA	(4)		(49)	[5]
Amortization of debt costs	(5)		1
Other	(2)		0
Total other noncash operating activities	36		42
Changes In Other Assets and Liabilities [Abstract]
Under/over-recovered energy and transmission costs	4		(18)
Other regulatory assets and liabilities	10		14
Other current assets and liabilities	(29)		17
Other noncurrent assets and liabilities	11		263
Total changes in other assets and liabilities	(24)		248
Cash Flow Noncash Investing And Financing Activities Disclosure [Abstract]
Allocation Of Tax Benefit From Parent	2
Indemnification of like-kind exchange position	(38)		0
Total noncash investing and financing activities	(2)		172
Commonwealth Edison Co [Member] | Indemnification Agreement [Member]
Cash Flow Noncash Investing And Financing Activities Disclosure [Abstract]
Indemnification of like-kind exchange position	2		(172)
PECO Energy Co [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment	56		55
Regulatory assets	2		2
Total depreciation, amortization and accretion	58		57
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefits costs	12		11
Provision for uncollectible accounts	35		25
Stock-based compensation costs	0		1
Amortization of regulatory asset related to debt costs	1		1
Amortization of debt costs	1		1
Other	0		0
Total other noncash operating activities	49		39
Changes In Other Assets and Liabilities [Abstract]
Under/over-recovered energy and transmission costs	(17)		22
Other regulatory assets and liabilities	3		(13)
Other current assets and liabilities	(105)		(75)
Other noncurrent assets and liabilities	(2)		2
Total changes in other assets and liabilities	(127)		(38)
DOE Smart Grid Investment Grant [Abstract]
Amount included in capital expenditures	2		6
Smart Grid Grant Reimbursements	2		12
Baltimore Gas and Electric Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment	70		64
Regulatory assets	38		29
Total depreciation, amortization and accretion	108		93
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefits costs	16		14
Provision for uncollectible accounts	11		4
Stock-based compensation costs	0		1
Amortization of regulatory asset related to debt costs	0		0
Amortization of rate stabilization deferral	20		30
Merger related commitments			(6)
Amortization of debt costs	0
Other	(4)		(1)
Total other noncash operating activities	43		42
Changes In Other Assets and Liabilities [Abstract]
Under/over-recovered energy and transmission costs	23		16
Other regulatory assets and liabilities	(6)		53
Other current assets and liabilities	18		73
Other noncurrent assets and liabilities	(3)		(2)
Total changes in other assets and liabilities	44		34
Cash Flow Noncash Investing And Financing Activities Disclosure [Abstract]
Indemnification of like-kind exchange position	0		0
DOE Smart Grid Investment Grant [Abstract]
Amount included in capital expenditures			15
Smart Grid Grant Reimbursements			$ 20

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

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

[3] 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 of the Exelon 2013 Form 10-K for additional information regarding the accounting for nuclear decommissioning.

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

[5] 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 4 - Regulatory Matters for more information.