Supplemental Financial Information - Cash Flow (Details) - USD ($) $ in Millions		3 Months Ended				6 Months Ended
		Jun. 30, 2018		Jun. 30, 2017		Jun. 30, 2018	Jun. 30, 2017
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]					$ 1,873	$ 1,545
Regulatory assets	[1]					278	238
Amortization of intangible assets, net	[1]					28	28
Amortization of Power Contracts Emission Credits	[2]					10	20
Amortization of Nuclear Fuel Lease	[3]					569	529
Asset Retirement Obligation, Accretion Expense	[4]					242	231
Total depreciation, amortization and accretion						3,000	2,591
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)		$ 145	[5]	$ 163	[5],[6]	290	320
Gain (loss) on equity method investments						12	19
Provision for uncollectible accounts						77	52
Stock-based compensation costs						47	57
Other Decommissioning Related Activity	[7]					(61)	(144)
Energy-related options	[8]					(7)	11
Amortization of regulatory asset related to debt costs						4	4
Amortization of rate stabilization deferral						13	(8)
Amortization of debt fair value adjustment						(7)	(9)
Discrete impacts from EIMA	[9]					14	(51)
Amortization of debt costs						18	49
Inventory Write-down						13	51
Employee Benefits and Share-based Compensation, Noncash						51
Merger related commitments							0
Restructuring Costs							25
Other						15	39
Total other noncash operating activities						479	415
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Capital Expenditures Incurred but Not yet Paid						283	105
Capitalized Costs, Asset Retirement Costs		47		103		47	103
Noncash or Part Noncash Acquisition, Fixed Assets Acquired							13
Stock Issued						3	3
Treasury Stock Reissued at Lower than Repurchase Price							1,054
Payments to Acquire Land						3
Exelon Generation Co L L C [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]					890	612
Regulatory assets	[1]					0	0
Amortization of intangible assets, net	[1]					24	25
Amortization of Power Contracts Emission Credits	[2]					10	20
Amortization of Nuclear Fuel Lease	[3]					569	529
Asset Retirement Obligation, Accretion Expense	[4]					242	229
Total depreciation, amortization and accretion						1,735	1,415
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)		51		59	[6]	100	113
Gain (loss) on equity method investments						12	19
Provision for uncollectible accounts						28	19
Stock-based compensation costs						0	0
Other Decommissioning Related Activity	[7]					(61)	(144)
Energy-related options	[8]					(7)	11
Amortization of regulatory asset related to debt costs						0	0
Amortization of rate stabilization deferral						0	0
Amortization of debt fair value adjustment						(6)	(6)
Discrete impacts from EIMA						0	0
Amortization of debt costs						7	30
Inventory Write-down						12	49
Employee Benefits and Share-based Compensation, Noncash						0
Merger related commitments							0
Restructuring Costs							17
Other						0	13
Total other noncash operating activities						85	121
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Capital Expenditures Incurred but Not yet Paid						310	48
Business Combination, Contingent Consideration, Liability, Noncurrent				49			49
Capitalized Costs, Asset Retirement Costs		47		103		47	103
Noncash or Part Noncash Acquisition, Fixed Assets Acquired							13
Stock Issued						0	0
Payments to Acquire Land						0
Commonwealth Edison Co [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]					406	384
Regulatory assets	[1]					53	35
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						459	419
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)		44		44		88	87
Gain (loss) on equity method investments						0	0
Provision for uncollectible accounts						18	15
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	2
Amortization of rate stabilization deferral						0	0
Amortization of debt fair value adjustment						0	0
Discrete impacts from EIMA	[9]					14	(51)
Amortization of debt costs						2	2
Inventory Write-down						1	1
Employee Benefits and Share-based Compensation, Noncash						0
Merger related commitments							0
Restructuring Costs							0
Other						(8)	2
Total other noncash operating activities						117	58
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Capital Expenditures Incurred but Not yet Paid						22	82
Capitalized Costs, Asset Retirement Costs		0		0		0	0
Contribution of Property	[10]						23
Noncash or Part Noncash Acquisition, Fixed Assets Acquired							0
Stock Issued						0	0
Payments to Acquire Land						0
PECO Energy Co [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]					135	129
Regulatory assets	[1]					14	12
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						149	141
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)		5		7		10	14
Gain (loss) on equity method investments						0	0
Provision for uncollectible accounts						11	9
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	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
Other						0	(2)
Total other noncash operating activities						22	22
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Capital Expenditures Incurred but Not yet Paid						17	44
Capitalized Costs, Asset Retirement Costs		0		0		0	0
Noncash or Part Noncash Acquisition, Fixed Assets Acquired							0
Stock Issued						0	0
Payments to Acquire Land						0
Baltimore Gas and Electric Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]					164	155
Regulatory assets	[1]					84	84
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						248	239
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)		15		16		29	31
Gain (loss) on equity method investments						0	0
Provision for uncollectible accounts						5	3
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
Other						(8)	(7)
Total other noncash operating activities						27	35
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Capital Expenditures Incurred but Not yet Paid						10	6
Capitalized Costs, Asset Retirement Costs		0		0		0	0
Noncash or Part Noncash Acquisition, Fixed Assets Acquired							0
Stock Issued						0	0
Payments to Acquire Land						0
Pepco Holdings LLC [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]					236	227
Regulatory assets	[1]					127	105
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						363	332
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)						34	48
Gain (loss) on equity method investments						0	0
Provision for uncollectible accounts						15	6
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	2
Amortization of rate stabilization deferral						13	(15)
Amortization of debt fair value adjustment						(1)	(3)
Discrete impacts from EIMA						0	0
Amortization of debt costs						3	0
Inventory Write-down						0	1
Employee Benefits and Share-based Compensation, Noncash						0
Merger related commitments	[11]						(8)
Restructuring Costs							3
Other						5	(6)
Total other noncash operating activities						71	28
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Capital Expenditures Incurred but Not yet Paid						61	8
Capitalized Costs, Asset Retirement Costs		0		0		0	0
Noncash or Part Noncash Acquisition, Fixed Assets Acquired							0
Stock Issued						0	0
Payments to Acquire Land						3
Potomac Electric Power Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]					107	101
Regulatory assets	[1]					81	59
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						188	160
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)		3		6		8	13
Gain (loss) on equity method investments						0	0
Provision for uncollectible accounts						7	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						1	1
Amortization of rate stabilization deferral						10	(10)
Amortization of debt fair value adjustment						0	0
Discrete impacts from EIMA						0	0
Amortization of debt costs						1	0
Inventory Write-down						0	0
Employee Benefits and Share-based Compensation, Noncash						0
Merger related commitments	[11]						(6)
Restructuring Costs							0
Other						(3)	(2)
Total other noncash operating activities						24	0
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Capital Expenditures Incurred but Not yet Paid						28	0
Capitalized Costs, Asset Retirement Costs		0		0		0	0
Noncash or Part Noncash Acquisition, Fixed Assets Acquired							0
Stock Issued						0	0
Payments to Acquire Land						0
Delmarva Power and Light Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]					64	61
Regulatory assets	[1]					24	18
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						88	79
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)		2		3		3	6
Gain (loss) on equity method investments						0	0
Provision for uncollectible accounts						2	0
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						3	(5)
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	[11]						(2)
Restructuring Costs							0
Other						5	(3)
Total other noncash operating activities						14	(3)
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Capital Expenditures Incurred but Not yet Paid						17	15
Capitalized Costs, Asset Retirement Costs		0		0		0	0
Noncash or Part Noncash Acquisition, Fixed Assets Acquired							0
Stock Issued						0	0
Payments to Acquire Land						0
Atlantic City Electric Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]					47	44
Regulatory assets	[1]					22	28
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						69	72
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)		3		3		6	7
Gain (loss) on equity method investments						0	0
Provision for uncollectible accounts						5	2
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	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
Other						1	(2)
Total other noncash operating activities						12	7
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Capital Expenditures Incurred but Not yet Paid						14	14
Capitalized Costs, Asset Retirement Costs		$ 0		$ 0		0	0
Noncash or Part Noncash Acquisition, Fixed Assets Acquired							0
Stock Issued						0	$ 0
Payments to Acquire Land						$ 3

[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] Exelon reflects the consolidated pension and other postretirement benefit costs of Generation, ComEd, PECO, BGE, BSC, and PHI. PHI reflects the consolidated pension and other postretirement benefit costs of Pepco, DPL, ACE, and PHISCO.

[6] FitzPatrick net benefit costs are included for the period after the acquisition date of March 31, 2017.

[7] 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 2017 Form 10-K for additional information regarding the accounting for nuclear decommissioning.

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

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

[10] See Note 12 - Income Taxes for discussion of the like-kind exchange tax position.

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