Supplemental Financial Information - Cash Flow (Details) - USD ($) $ in Millions		3 Months Ended	9 Months Ended
		Sep. 30, 2018	Sep. 30, 2018	Sep. 30, 2017
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]		$ 2,829	$ 2,416
Regulatory assets	[1]		412	355
Amortization of intangible assets, net	[1]		43	43
Amortization of Power Contracts Emission Credits	[2]		8	19
Amortization of Nuclear Fuel Lease	[3]		852	816
Asset Retirement Obligation, Accretion Expense	[4]		367	350
Total depreciation, amortization and accretion			4,511	3,999
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)			435	482
Gain (loss) on equity method investments			22	26
Provision for uncollectible accounts			133	103
Stock-based compensation costs			64	76
Other Decommissioning Related Activity	[5]		(39)	(213)
Energy-related options	[6]		4	15
Amortization of regulatory asset related to debt costs			6	7
Amortization of rate stabilization deferral			0	(7)
Amortization of debt fair value adjustment			(12)	(13)
Discrete impacts from EIMA	[7]		27	(61)
Amortization of debt costs			26	57
Inventory Write-down			15	52
Employee Benefits and Share-based Compensation, Noncash			84
Merger related commitments				0
Restructuring Costs				33
Asset Retirement Obligation, Revision of Estimate			20
Other			19	46
Total other noncash operating activities			804	603
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Increase (Decrease) in capital expenditures not paid			175	101
Increase (Decrease) in PPE related to ARO update		$ 67	67	141
Noncash or Part Noncash Acquisition, Fixed Assets Acquired				16
Stock Issued			4	5
Payments to Acquire Land			3
Non Cash Dissolution of Financing Trust Due to Long-term Debt Retirement				8
Fair value adjustment of long-term debt due to retirement				(5)
Exelon Generation Co L L C [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]		1,347	1,010
Regulatory assets	[1]		0	0
Amortization of intangible assets, net	[1]		36	36
Amortization of Power Contracts Emission Credits	[2]		8	19
Amortization of Nuclear Fuel Lease	[3]		852	816
Asset Retirement Obligation, Accretion Expense	[4]		365	350
Total depreciation, amortization and accretion			2,608	2,231
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)			151	170
Gain (loss) on equity method investments			23	26
Provision for uncollectible accounts			38	31
Stock-based compensation costs			0	0
Other Decommissioning Related Activity	[5]		(39)	(213)
Energy-related options	[6]		4	15
Amortization of regulatory asset related to debt costs			0	0
Amortization of rate stabilization deferral			0	0
Amortization of debt fair value adjustment			(9)	(9)
Discrete impacts from EIMA			0	0
Amortization of debt costs			10	33
Inventory Write-down			13	50
Employee Benefits and Share-based Compensation, Noncash			0
Merger related commitments				0
Restructuring Costs				25
Asset Retirement Obligation, Revision of Estimate		(84)	0
Other			(4)	4
Total other noncash operating activities			187	132
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Increase (Decrease) in capital expenditures not paid			226	20
Business Combination, Contingent Consideration, Liability, Noncurrent				33
Increase (Decrease) in PPE related to ARO update		47	47	141
Noncash or Part Noncash Acquisition, Fixed Assets Acquired				16
Stock Issued			0	0
Payments to Acquire Land			0
Non Cash Dissolution of Financing Trust Due to Long-term Debt Retirement				0
Commonwealth Edison Co [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]		613	579
Regulatory assets	[1]		83	52
Amortization of intangible assets, net	[1]		0	0
Amortization of Power Contracts Emission Credits	[2]		0	0
Amortization of Nuclear Fuel Lease	[3]		0	0
Asset Retirement Obligation, Accretion Expense	[4]		0	0
Total depreciation, amortization and accretion			696	631
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)			133	131
Gain (loss) on equity method investments			0	0
Provision for uncollectible accounts			30	25
Stock-based compensation costs			0	0
Other Decommissioning Related Activity			0	0
Energy-related options			0	0
Amortization of regulatory asset related to debt costs			2	3
Amortization of rate stabilization deferral			0	0
Amortization of debt fair value adjustment			0	0
Discrete impacts from EIMA	[7]		27	(61)
Amortization of debt costs			4	3
Inventory Write-down			2	1
Employee Benefits and Share-based Compensation, Noncash			0
Merger related commitments				0
Restructuring Costs				0
Asset Retirement Obligation, Revision of Estimate			0
Other			(11)	10
Total other noncash operating activities			187	112
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Increase (Decrease) in capital expenditures not paid			28	79
Increase (Decrease) in PPE related to ARO update		4	4	0
Contribution of Property	[8]			21
Noncash or Part Noncash Acquisition, Fixed Assets Acquired				0
Stock Issued			0	0
Payments to Acquire Land			0
Non Cash Dissolution of Financing Trust Due to Long-term Debt Retirement				0
PECO Energy Co [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]		204	194
Regulatory assets	[1]		20	19
Amortization of intangible assets, net	[1]		0	0
Amortization of Power Contracts Emission Credits	[2]		0	0
Amortization of Nuclear Fuel Lease	[3]		0	0
Asset Retirement Obligation, Accretion Expense	[4]		0	0
Total depreciation, amortization and accretion			224	213
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)			14	21
Gain (loss) on equity method investments			0	0
Provision for uncollectible accounts			25	17
Stock-based compensation costs			0	0
Other Decommissioning Related Activity			0	0
Energy-related options			0	0
Amortization of regulatory asset related to debt costs			0	1
Amortization of rate stabilization deferral			0	0
Amortization of debt fair value adjustment			0	0
Discrete impacts from EIMA			0	0
Amortization of debt costs			1	1
Inventory Write-down			0	0
Employee Benefits and Share-based Compensation, Noncash			0
Merger related commitments				0
Restructuring Costs				0
Asset Retirement Obligation, Revision of Estimate			0
Other			1	(2)
Total other noncash operating activities			41	38
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Increase (Decrease) in capital expenditures not paid			4	29
Increase (Decrease) in PPE related to ARO update		0	0	0
Noncash or Part Noncash Acquisition, Fixed Assets Acquired				0
Stock Issued			0	0
Payments to Acquire Land			0
Non Cash Dissolution of Financing Trust Due to Long-term Debt Retirement				0
Baltimore Gas and Electric Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]		249	233
Regulatory assets	[1]		109	115
Amortization of intangible assets, net	[1]		0	0
Amortization of Power Contracts Emission Credits	[2]		0	0
Amortization of Nuclear Fuel Lease	[3]		0	0
Asset Retirement Obligation, Accretion Expense	[4]		0	0
Total depreciation, amortization and accretion			358	348
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)			43	47
Gain (loss) on equity method investments			0	0
Provision for uncollectible accounts			6	4
Stock-based compensation costs			0	0
Other Decommissioning Related Activity			0	0
Energy-related options			0	0
Amortization of regulatory asset related to debt costs			0	0
Amortization of rate stabilization deferral			0	7
Amortization of debt fair value adjustment			0	0
Discrete impacts from EIMA			0	0
Amortization of debt costs			1	1
Inventory Write-down			0	0
Employee Benefits and Share-based Compensation, Noncash			0
Merger related commitments				0
Restructuring Costs				0
Asset Retirement Obligation, Revision of Estimate			0
Other			(8)	(7)
Total other noncash operating activities			42	52
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Increase (Decrease) in capital expenditures not paid			44	16
Increase (Decrease) in PPE related to ARO update		1	1	0
Noncash or Part Noncash Acquisition, Fixed Assets Acquired				0
Stock Issued			0	0
Payments to Acquire Land			0
Non Cash Dissolution of Financing Trust Due to Long-term Debt Retirement				8
Pepco Holdings LLC [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]		355	342
Regulatory assets	[1]		200	169
Amortization of intangible assets, net	[1]		0	0
Amortization of Power Contracts Emission Credits	[2]		0	0
Amortization of Nuclear Fuel Lease	[3]		0	0
Asset Retirement Obligation, Accretion Expense	[4]		0	0
Total depreciation, amortization and accretion			555	511
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)			51	72
Gain (loss) on equity method investments			(1)	0
Provision for uncollectible accounts			32	26
Stock-based compensation costs			0	0
Other Decommissioning Related Activity			0	0
Energy-related options			0	0
Amortization of regulatory asset related to debt costs			3	3
Amortization of rate stabilization deferral			0	(14)
Amortization of debt fair value adjustment			(3)	(4)
Discrete impacts from EIMA			0	0
Amortization of debt costs			3	1
Inventory Write-down			0	1
Employee Benefits and Share-based Compensation, Noncash			0
Merger related commitments	[9]			(8)
Restructuring Costs				3
Asset Retirement Obligation, Revision of Estimate			20
Other			4	(14)
Total other noncash operating activities			109	66
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Increase (Decrease) in capital expenditures not paid			54	6
Increase (Decrease) in PPE related to ARO update		15	15
Noncash or Part Noncash Acquisition, Fixed Assets Acquired				0
Stock Issued			0	0
Payments to Acquire Land			3
Non Cash Dissolution of Financing Trust Due to Long-term Debt Retirement				0
Potomac Electric Power Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]		161	153
Regulatory assets	[1]		125	89
Amortization of intangible assets, net	[1]		0	0
Amortization of Power Contracts Emission Credits	[2]		0	0
Amortization of Nuclear Fuel Lease	[3]		0	0
Asset Retirement Obligation, Accretion Expense	[4]		0	0
Total depreciation, amortization and accretion			286	242
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)			10	19
Gain (loss) on equity method investments			0	0
Provision for uncollectible accounts			12	11
Stock-based compensation costs			0	0
Other Decommissioning Related Activity			0	0
Energy-related options			0	0
Amortization of regulatory asset related to debt costs			1	1
Amortization of rate stabilization deferral			0	(12)
Amortization of debt fair value adjustment			0	0
Discrete impacts from EIMA			0	0
Amortization of debt costs			2	1
Inventory Write-down			0	0
Employee Benefits and Share-based Compensation, Noncash			0
Merger related commitments	[9]			(6)
Restructuring Costs				0
Asset Retirement Obligation, Revision of Estimate			22
Other			(5)	(6)
Total other noncash operating activities			42	8
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Increase (Decrease) in capital expenditures not paid			15	7
Increase (Decrease) in PPE related to ARO update		12	12
Noncash or Part Noncash Acquisition, Fixed Assets Acquired				0
Stock Issued			0	0
Payments to Acquire Land			0
Non Cash Dissolution of Financing Trust Due to Long-term Debt Retirement				0
Delmarva Power and Light Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]		97	92
Regulatory assets	[1]		38	32
Amortization of intangible assets, net	[1]		0	0
Amortization of Power Contracts Emission Credits	[2]		0	0
Amortization of Nuclear Fuel Lease	[3]		0	0
Asset Retirement Obligation, Accretion Expense	[4]		0	0
Total depreciation, amortization and accretion			135	124
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)			5	10
Gain (loss) on equity method investments			0	0
Provision for uncollectible accounts			6	1
Stock-based compensation costs			0	0
Other Decommissioning Related Activity			0	0
Energy-related options			0	0
Amortization of regulatory asset related to debt costs			1	1
Amortization of rate stabilization deferral			0	(2)
Amortization of debt fair value adjustment			0	0
Discrete impacts from EIMA			0	0
Amortization of debt costs			1	0
Inventory Write-down			0	1
Employee Benefits and Share-based Compensation, Noncash			0
Merger related commitments	[9]			(2)
Restructuring Costs				0
Asset Retirement Obligation, Revision of Estimate			(1)
Other			4	(3)
Total other noncash operating activities			16	6
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Increase (Decrease) in capital expenditures not paid			20	14
Increase (Decrease) in PPE related to ARO update		2	2	0
Noncash or Part Noncash Acquisition, Fixed Assets Acquired				0
Stock Issued			0	0
Payments to Acquire Land			0
Non Cash Dissolution of Financing Trust Due to Long-term Debt Retirement				0
Atlantic City Electric Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]		70	66
Regulatory assets	[1]		37	47
Amortization of intangible assets, net	[1]		0	0
Amortization of Power Contracts Emission Credits	[2]		0	0
Amortization of Nuclear Fuel Lease	[3]		0	0
Asset Retirement Obligation, Accretion Expense	[4]		0	0
Total depreciation, amortization and accretion			107	113
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)			10	10
Gain (loss) on equity method investments			0	0
Provision for uncollectible accounts			14	14
Stock-based compensation costs			0	0
Other Decommissioning Related Activity			0	0
Energy-related options			0	0
Amortization of regulatory asset related to debt costs			1	1
Amortization of rate stabilization deferral			0	0
Amortization of debt fair value adjustment			0	0
Discrete impacts from EIMA			0	0
Amortization of debt costs			0	0
Inventory Write-down			0	0
Employee Benefits and Share-based Compensation, Noncash			0
Merger related commitments				0
Restructuring Costs				0
Asset Retirement Obligation, Revision of Estimate			(1)
Other			0	(4)
Total other noncash operating activities			24	21
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Increase (Decrease) in capital expenditures not paid			16	18
Increase (Decrease) in PPE related to ARO update		$ 1	1
Noncash or Part Noncash Acquisition, Fixed Assets Acquired				0
Stock Issued			0	0
Payments to Acquire Land			$ 3
Non Cash Dissolution of Financing Trust Due to Long-term Debt Retirement				$ 0

[1] Included in Depreciation and amortization on the Registrants' Consolidated Statements of Operations and Comprehensive Income.

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

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

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

[5] Includes the elimination of decommissioning-related activities 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 2017 Form 10-K for additional information regarding the accounting for nuclear decommissioning.

[6] Includes option premiums reclassified to realized at the settlement of the underlying contracts and recorded in Operating revenues and expenses.

[7] Reflects the change in ComEd's distribution and energy efficiency formula rates. See Note 6 — Regulatory Matters for additional information.

[8] See Note 12 - Income Taxes for additional information on the like-kind exchange tax position.

[9] See Note 4 - Mergers, Acquisitions and Dispositions for additional information.