Supplemental Financial Information - Cash Flow (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]	$ 917	$ 926
Amortization of regulatory assets	[1]	143	152
Amortization of intangible assets, net	[1]	15	13
Amortization of energy contract assets and liabilities	[2]		3
Amortization of nuclear fuel	[3]	261	287
ARO accretion	[4]	124	120
Total depreciation, amortization and accretion		1,460	1,501
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs		106	145
Loss on equity method investments		6	7
Provision for uncollectible accounts		43	64
Stock-based compensation costs		28	29
Other decommissioning-related activity	[5]	(202)	(31)
Energy-related options	[6]	37	(7)
Amortization of regulatory asset related to debt costs		3	2
Amortization of rate stabilization deferral		(6)	7
Amortization of debt fair value adjustment		(4)	(3)
Discrete impacts from EIMA and FEJA	[7]	28	(4)
Amortization of debt costs		9	9
Provision for excess and obsolete inventory			13
Long-term incentive plan		25
Amortization of operating ROU asset		53
Other		1	9
Total other noncash operating activities		127	240
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Change in capital expenditures not paid		(229)	(177)
Change in PPE related to ARO update		301	32
Dividends on stock compensation		1	1
Exelon Generation Co L L C [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]	392	436
Amortization of regulatory assets	[1]	0	0
Amortization of intangible assets, net	[1]	13	12
Amortization of energy contract assets and liabilities	[2]		3
Amortization of nuclear fuel	[3]	261	287
ARO accretion	[4]	123	120
Total depreciation, amortization and accretion		789	858
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs		31	51
Loss on equity method investments		6	7
Provision for uncollectible accounts		0	11
Other decommissioning-related activity	[5]	(202)	(31)
Energy-related options	[6]	37	(7)
Amortization of regulatory asset related to debt costs		0	0
Amortization of rate stabilization deferral		0	0
Amortization of debt fair value adjustment		(3)	(3)
Amortization of debt costs		3	3
Provision for excess and obsolete inventory			12
Amortization of operating ROU asset		34
Other		4	2
Total other noncash operating activities		(90)	45
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Change in capital expenditures not paid		(93)	(131)
Change in PPE related to ARO update		301	32
Commonwealth Edison Co [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]	219	201
Amortization of regulatory assets	[1]	32	27
Amortization of intangible assets, net	[1]	0	0
ARO accretion	[4]	0	0
Total depreciation, amortization and accretion		251	228
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs		24	45
Loss on equity method investments		0	0
Provision for uncollectible accounts		9	8
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 and FEJA	[7]	28	(4)
Amortization of debt costs		1	1
Provision for excess and obsolete inventory			1
Amortization of operating ROU asset		1
Other		(7)	(6)
Total other noncash operating activities		56	46
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Change in capital expenditures not paid		(80)	(48)
Change in PPE related to ARO update		0	0
PECO Energy Co [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]	74	68
Amortization of regulatory assets	[1]	7	7
Amortization of intangible assets, net	[1]	0	0
ARO accretion	[4]	0	0
Total depreciation, amortization and accretion		81	75
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs		2	5
Loss on equity method investments		0	0
Provision for uncollectible accounts		16	17
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
Amortization of debt costs		0	0
Provision for excess and obsolete inventory			0
Amortization of operating ROU asset		0
Other		(2)	(1)
Total other noncash operating activities		16	21
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Change in capital expenditures not paid		8	(25)
Change in PPE related to ARO update		0	0
Baltimore Gas and Electric Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]	85	82
Amortization of regulatory assets	[1]	51	52
Amortization of intangible assets, net	[1]	0	0
ARO accretion	[4]	0	0
Total depreciation, amortization and accretion		136	134
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs		15	14
Loss on equity method investments		0	0
Provision for uncollectible accounts		8	8
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
Amortization of debt costs		0	0
Provision for excess and obsolete inventory			0
Amortization of operating ROU asset		8
Other		(4)	(2)
Total other noncash operating activities		27	20
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Change in capital expenditures not paid		2	(11)
Change in PPE related to ARO update		0	0
Pepco Holdings LLC [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]	127	117
Amortization of regulatory assets	[1]	53	66
Amortization of intangible assets, net	[1]	0	0
ARO accretion	[4]	0	0
Total depreciation, amortization and accretion		180	183
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs		23	15
Loss on equity method investments		0	0
Provision for uncollectible accounts		10	20
Amortization of regulatory asset related to debt costs		1	1
Amortization of rate stabilization deferral		(6)	7
Amortization of debt fair value adjustment		(1)	0
Amortization of debt costs		1	1
Provision for excess and obsolete inventory			0
Amortization of operating ROU asset		9
Other		(2)	9
Total other noncash operating activities		35	53
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Change in capital expenditures not paid		(55)	61
Change in PPE related to ARO update		0	0
Potomac Electric Power Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]	58	53
Amortization of regulatory assets	[1]	36	43
Amortization of intangible assets, net	[1]	0	0
ARO accretion	[4]	0	0
Total depreciation, amortization and accretion		94	96
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs		6	4
Loss on equity method investments		0	0
Provision for uncollectible accounts		4	6
Amortization of regulatory asset related to debt costs		0	0
Amortization of rate stabilization deferral		(7)	1
Amortization of debt fair value adjustment		0	0
Amortization of debt costs		1	0
Provision for excess and obsolete inventory			0
Amortization of operating ROU asset		2
Other		(3)	(1)
Total other noncash operating activities		3	10
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Change in capital expenditures not paid		(15)	19
Change in PPE related to ARO update		0	0
Delmarva Power and Light Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]	35	32
Amortization of regulatory assets	[1]	11	13
Amortization of intangible assets, net	[1]	0	0
ARO accretion	[4]	0	0
Total depreciation, amortization and accretion		46	45
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs		4	0
Loss on equity method investments		0	0
Provision for uncollectible accounts		4	8
Amortization of regulatory asset related to debt costs		0	0
Amortization of rate stabilization deferral		1	6
Amortization of debt fair value adjustment		0	0
Amortization of debt costs		0	0
Provision for excess and obsolete inventory			0
Amortization of operating ROU asset		2
Other		0	5
Total other noncash operating activities		11	19
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Change in capital expenditures not paid		(17)	14
Change in PPE related to ARO update		0	0
Atlantic City Electric Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]	25	23
Amortization of regulatory assets	[1]	6	10
Amortization of intangible assets, net	[1]	0	0
ARO accretion	[4]	0	0
Total depreciation, amortization and accretion		31	33
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs		4	3
Loss on equity method investments		0	0
Provision for uncollectible accounts		2	5
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
Amortization of debt costs		0	0
Provision for excess and obsolete inventory			0
Amortization of operating ROU asset		1
Other		(2)	1
Total other noncash operating activities		5	9
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Change in capital expenditures not paid		(24)	27
Change in PPE related to ARO update		$ 0	$ 0

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

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

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

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

[5] Includes the elimination of decommissioning-related 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 2018 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.