Supplemental Financial Information - Supplemental Cash Flow Information (Details) - USD ($)		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014		Dec. 31, 2013
Supplemental Cash Flow Information [Line Items]
Interest (net of amount capitalized)		$ 930,000,000	$ 940,000,000		$ 866,000,000
Income taxes (net of refunds)		342,000,000	314,000,000		112,000,000
Pension and non-pension postretirement benefit costs		637,000,000	560,000,000		825,000,000
Income (Loss) from Equity Method Investments			20,000,000		(10,000,000)
Provision for uncollectible accounts		120,000,000	156,000,000		101,000,000
Provision for excess and obsolete inventory		10,000,000	5,000,000		9,000,000
Stock-based compensation costs		97,000,000	91,000,000		120,000,000
Other decommissioning related-activity		(82,000,000)	(132,000,000)		(169,000,000)
Energy-related options		21,000,000	122,000,000		104,000,000
Amortization of regulatory asset related to debt costs		7,000,000	11,000,000		12,000,000
Amortization of rate stabilization deferral		73,000,000	65,000,000		66,000,000
Amortization of debt fair value adjustment		(17,000,000)	(23,000,000)		(34,000,000)
Merger-related commitments			44,000,000
Discrete impacts from EIMA		144,000,000	53,000,000		(271,000,000)
Amortization of debt costs		58,000,000	53,000,000		18,000,000
Lower of cost or market inventory adjustment		23,000,000	29,000,000
Other		11,000,000	(2,000,000)		(53,000,000)
Total other non-cash operating activities		1,109,000,000	1,054,000,000		718,000,000
Total changes in other assets and liabilities		387,000,000	157,000,000		(128,000,000)
Change in PPE related to ARO update		885,000,000	72,000,000		(128,000,000)
Change in capital expenditures not paid		96,000,000	220,000,000		(38,000,000)
Consolidated VIE dividend to noncontrolling			421,000,000
Noncash Purchase Accounting Adjustment			3,400,000,000
Fair value of net assets recorded upon CENG consolidation			(131,000,000)
Indemnification of like-kind exchange position					0
Other Cost and Expense, Operating		8,322,000,000	8,568,000,000		7,270,000,000
Non Cash Licensing Agreement	[1]	95,000,000
Antelope Valle [Member]
Supplemental Cash Flow Information [Line Items]
Change in capital expenditures not paid			170,000,000
Nuclear Fuel Project [Member]
Supplemental Cash Flow Information [Line Items]
Noncash or Part Noncash Acquisition, Fixed Assets Acquired	[2]	57,000,000
Capital Project [Member]
Supplemental Cash Flow Information [Line Items]
Noncash or Part Noncash Acquisition, Fixed Assets Acquired		77,000,000
Indemnification Agreement [Member]
Supplemental Cash Flow Information [Line Items]
Noncash or Part Noncash Acquisition, Fixed Assets Acquired			70,000,000
Indemnification of like-kind exchange position		0	0
Exelon Generation Co L L C [Member]
Supplemental Cash Flow Information [Line Items]
Interest (net of amount capitalized)		348,000,000	322,000,000		291,000,000
Income taxes (net of refunds)		476,000,000	227,000,000		(18,000,000)
Pension and non-pension postretirement benefit costs		269,000,000	249,000,000		345,000,000
Income (Loss) from Equity Method Investments		(8,000,000)	20,000,000		(10,000,000)
Provision for uncollectible accounts		22,000,000	14,000,000		10,000,000
Provision for excess and obsolete inventory		9,000,000	5,000,000		9,000,000
Stock-based compensation costs		0	0		0
Other decommissioning related-activity		(82,000,000)	(132,000,000)		(169,000,000)
Energy-related options		21,000,000	122,000,000		104,000,000
Amortization of regulatory asset related to debt costs		0	0		0
Amortization of rate stabilization deferral		0	0		0
Amortization of debt fair value adjustment		(17,000,000)	(23,000,000)		(34,000,000)
Merger-related commitments			44,000,000
Discrete impacts from EIMA		0	0		0
Amortization of debt costs		15,000,000	12,000,000		10,000,000
Lower of cost or market inventory adjustment		23,000,000	29,000,000
Other		0	6,000,000		5,000,000
Total other non-cash operating activities		268,000,000	346,000,000		270,000,000
Total changes in other assets and liabilities		207,000,000	(57,000,000)		85,000,000
Change in PPE related to ARO update		885,000,000	72,000,000		(128,000,000)
Change in capital expenditures not paid		82,000,000	(61,000,000)		(107,000,000)
Consolidated VIE dividend to noncontrolling					63,000,000
Noncash Purchase Accounting Adjustment			3,400,000,000
Indemnification of like-kind exchange position					0
Other Cost and Expense, Operating		4,688,000,000	4,943,000,000		3,960,000,000
Exelon Generation Co L L C [Member] | Nuclear Fuel Project [Member]
Supplemental Cash Flow Information [Line Items]
Noncash or Part Noncash Acquisition, Fixed Assets Acquired	[2]	57,000,000
Exelon Generation Co L L C [Member] | Capital Project [Member]
Supplemental Cash Flow Information [Line Items]
Noncash or Part Noncash Acquisition, Fixed Assets Acquired		77,000,000
Exelon Generation Co L L C [Member] | Indemnification Agreement [Member]
Supplemental Cash Flow Information [Line Items]
Noncash or Part Noncash Acquisition, Fixed Assets Acquired			70,000,000
Indemnification of like-kind exchange position		0	0
Commonwealth Edison Co [Member]
Supplemental Cash Flow Information [Line Items]
Interest (net of amount capitalized)		308,000,000	292,000,000		283,000,000
Income taxes (net of refunds)		(265,000,000)	(6,000,000)		33,000,000
Pension and non-pension postretirement benefit costs		206,000,000	162,000,000		308,000,000
Income (Loss) from Equity Method Investments		0	0		0
Provision for uncollectible accounts		53,000,000	26,000,000		(15,000,000)
Provision for excess and obsolete inventory		1,000,000	0		0
Stock-based compensation costs		0	0		0
Other decommissioning related-activity		0	0		0
Energy-related options		0	0		0
Amortization of regulatory asset related to debt costs		5,000,000	8,000,000		9,000,000
Amortization of rate stabilization deferral		0	0		0
Amortization of debt fair value adjustment		0	0		0
Merger-related commitments			0
Discrete impacts from EIMA		144,000,000	53,000,000		(271,000,000)
Amortization of debt costs		4,000,000	4,000,000		1,000,000
Lower of cost or market inventory adjustment		0
Other		3,000,000	2,000,000		(4,000,000)
Total other non-cash operating activities		416,000,000	255,000,000		28,000,000
Total changes in other assets and liabilities		(69,000,000)	(1,000,000)		(171,000,000)
Change in PPE related to ARO update		0	0		0
Change in capital expenditures not paid		34,000,000	78,000,000		(8,000,000)
Issuance of equity units			0
Indemnification of like-kind exchange position		202,000,000	273,000,000		176,000,000
Other Cost and Expense, Operating		1,372,000,000	1,263,000,000		1,211,000,000
Commonwealth Edison Co [Member] | Indemnification Agreement [Member]
Supplemental Cash Flow Information [Line Items]
Energy-related options		0
Indemnification of like-kind exchange position		7,000,000	5,000,000
PECO Energy Co [Member]
Supplemental Cash Flow Information [Line Items]
Interest (net of amount capitalized)		94,000,000	94,000,000		95,000,000
Income taxes (net of refunds)		64,000,000	85,000,000		70,000,000
Pension and non-pension postretirement benefit costs		39,000,000	36,000,000		43,000,000
Income (Loss) from Equity Method Investments		0	0		0
Provision for uncollectible accounts		30,000,000	52,000,000		61,000,000
Provision for excess and obsolete inventory		0	0		0
Stock-based compensation costs		0	0		0
Other decommissioning related-activity		0	0		0
Energy-related options		0	0		0
Amortization of regulatory asset related to debt costs		2,000,000	3,000,000		3,000,000
Amortization of rate stabilization deferral		0	0		0
Amortization of debt fair value adjustment		0	0		0
Merger-related commitments			0
Discrete impacts from EIMA		0	0		0
Amortization of debt costs		2,000,000	2,000,000		2,000,000
Lower of cost or market inventory adjustment		0
Other		(3,000,000)	(1,000,000)		(1,000,000)
Total other non-cash operating activities		70,000,000	92,000,000		108,000,000
Total changes in other assets and liabilities		4,000,000	21,000,000		(4,000,000)
Change in PPE related to ARO update		0	0		0
Change in capital expenditures not paid		(13,000,000)	0		13,000,000
Issuance of equity units			0
Indemnification of like-kind exchange position		16,000,000	24,000,000		27,000,000
Other Cost and Expense, Operating		684,000,000	767,000,000		647,000,000
PECO Energy Co [Member] | Indemnification Agreement [Member]
Supplemental Cash Flow Information [Line Items]
Energy-related options		0
Indemnification of like-kind exchange position		0	0
Baltimore Gas and Electric Company [Member]
Supplemental Cash Flow Information [Line Items]
Interest (net of amount capitalized)		120,000,000	111,000,000		130,000,000
Income taxes (net of refunds)		73,000,000	(21,000,000)		42,000,000
Pension and non-pension postretirement benefit costs		65,000,000	64,000,000		56,000,000
Income (Loss) from Equity Method Investments		0	0		0
Provision for uncollectible accounts		15,000,000	64,000,000		44,000,000
Provision for excess and obsolete inventory		0	0		0
Stock-based compensation costs		0	0		0
Other decommissioning related-activity		0	0	[3]	0	[4]
Energy-related options		0	0	[5]	0	[6]
Amortization of regulatory asset related to debt costs		0	0		0
Amortization of rate stabilization deferral		73,000,000	65,000,000		66,000,000
Amortization of debt fair value adjustment		0	0		0
Merger-related commitments			0
Discrete impacts from EIMA		0	0	[7]	0	[8]
Amortization of debt costs		2,000,000	2,000,000		2,000,000
Lower of cost or market inventory adjustment		0
Other		(18,000,000)	(15,000,000)		(15,000,000)
Total other non-cash operating activities		137,000,000	180,000,000		153,000,000
Total changes in other assets and liabilities		173,000,000	158,000,000		72,000,000
Change in PPE related to ARO update		0	0		4,000,000
Change in capital expenditures not paid		(9,000,000)	25,000,000		48,000,000
Noncash Purchase Accounting Adjustment			0
Issuance of equity units			0
Indemnification of like-kind exchange position		7,000,000	0		0
Other Cost and Expense, Operating		565,000,000	614,000,000		551,000,000
Baltimore Gas and Electric Company [Member] | Indemnification Agreement [Member]
Supplemental Cash Flow Information [Line Items]
Energy-related options		0
Indemnification of like-kind exchange position		0	0	[9]
Exelon Consolidations [Member]
Supplemental Cash Flow Information [Line Items]
Income (Loss) from Equity Method Investments		$ (7,000,000)	$ 22,000,000
Constellation Energy Group Acquisition [Member]
Supplemental Cash Flow Information [Line Items]
Consolidated VIE dividend to noncontrolling					63,000,000
Constellation Energy Group Acquisition [Member] | Exelon Generation Co L L C [Member]
Supplemental Cash Flow Information [Line Items]
Consolidated VIE dividend to noncontrolling					63,000,000
Constellation Energy Group Acquisition [Member] | Commonwealth Edison Co [Member]
Supplemental Cash Flow Information [Line Items]
Consolidated VIE dividend to noncontrolling					0
Constellation Energy Group Acquisition [Member] | PECO Energy Co [Member]
Supplemental Cash Flow Information [Line Items]
Consolidated VIE dividend to noncontrolling					0
Constellation Energy Group Acquisition [Member] | Baltimore Gas and Electric Company [Member]
Supplemental Cash Flow Information [Line Items]
Consolidated VIE dividend to noncontrolling					$ 0

[1] (f)Relates to a long-term software license agreement entered into on May 30, 2015. Exelon is required to make payments starting August of 2015 through May of 2024. See Note 14 — Debt and Credit Agreements for additional information.

[2] (d)Relates to the nuclear fuel procurement contract for the purchase of fixed quantities of converted uranium, which was delivered to Generation in 2015. Generation is required to make payments starting September 28, 2018, with the final payment being due no later than September 30, 2020.

[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 16 — Asset Retirement Obligations for additional information regarding the accounting for nuclear decommissioning.

[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 16 — Asset Retirement Obligations 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] Includes option premiums reclassified to realized at the settlement of the underlying contracts and recorded to results of operations.

[7] 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 3 — Regulatory Matters for more information.

[8] (d)Includes $55 million of changes in capital expenditures not paid between December 31, 2013 and 2012 related to Antelope Valley.

[9] Relates to the present value of the contract payments for the equity units issued by Exelon. See Note 20 — Stock-Based Compensation Plans for additional information.