Supplemental Financial Information Supplemental Financial Information - Summary of Other Income (Expense) (Details) - USD ($) $ in Millions		3 Months Ended	9 Months Ended	12 Months Ended
		Mar. 23, 2016	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Decommissioning-Related Activities [Abstract]
Net realized income on NDT funds - Regulatory agreement units	[1]			$ 506	$ 488	$ 237
Net realized income on NDT funds - Non-regulatory agreement units	[1]			302	209	126
Net unrealized gains (losses) on NDT funds - Regulatory agreement units				(715)	455	216
Net unrealized gains (losses) on NDT funds - Non-regulatory agreement				(483)	521	194
Net unrealized income (losses) on pledged assets				(8)	(10)	(1)
Regulatory offset to NDT fund-related activities	[2]			171	(724)	(372)
Total decommissioning-related activities				(227)	939	400
Investment income (loss)				43	8	17
Long-term lease income						4
Interest income (expense) related to uncertain income tax positions				5	3	13
Benefit (penalty) related to uncertain income tax positions	[3]				2	(106)
AFUDC—Equity				69	73	64
Non-service net periodic benefit cost				(47)	(109)	(116)
Loss on debt extinguishment						(3)
Other				45	31	24
Other, net				(112)	947	297
Exelon Generation Co L L C [Member]
Decommissioning-Related Activities [Abstract]
Net realized income on NDT funds - Regulatory agreement units	[1]			506	488	237
Net realized income on NDT funds - Non-regulatory agreement units	[1]			302	209	126
Net unrealized gains (losses) on NDT funds - Regulatory agreement units				(715)	455	216
Net unrealized gains (losses) on NDT funds - Non-regulatory agreement				(483)	521	194
Net unrealized income (losses) on pledged assets				(8)	(10)	(1)
Regulatory offset to NDT fund-related activities	[2]			171	(724)	(372)
Total decommissioning-related activities				(227)	939	400
Investment income (loss)				32	6	8
Long-term lease income						0
Interest income (expense) related to uncertain income tax positions				1	(1)	0
Benefit (penalty) related to uncertain income tax positions	[3]				0	0
AFUDC—Equity				0	0	0
Loss on debt extinguishment						(2)
Other				16	4	(5)
Other, net				(178)	948	401
Commonwealth Edison Co [Member]
Decommissioning-Related Activities [Abstract]
Investment income (loss)				0	0	0
Long-term lease income						0
Interest income (expense) related to uncertain income tax positions				0	0	0
Benefit (penalty) related to uncertain income tax positions	[3]				0	(86)
AFUDC—Equity				19	12	14
Loss on debt extinguishment						0
Other				14	10	7
Other, net				33	22	(65)
PECO Energy Co [Member]
Decommissioning-Related Activities [Abstract]
Investment income (loss)				1	0	(1)
Long-term lease income						0
Interest income (expense) related to uncertain income tax positions				0	0	0
Benefit (penalty) related to uncertain income tax positions	[3]				0	0
AFUDC—Equity				7	9	8
Loss on debt extinguishment						0
Other				0	0	1
Other, net				8	9	8
Baltimore Gas and Electric Company [Member]
Decommissioning-Related Activities [Abstract]
Investment income (loss)				1	0	2
Long-term lease income						0
Interest income (expense) related to uncertain income tax positions				0	0	0
Benefit (penalty) related to uncertain income tax positions	[3]				0	0
AFUDC—Equity				18	16	19
Loss on debt extinguishment						0
Other				0	0	0
Other, net				19	16	21
Pepco Holdings LLC [Member]
Decommissioning-Related Activities [Abstract]
Investment income (loss)				4	2
Interest income (expense) related to uncertain income tax positions				0	0
Benefit (penalty) related to uncertain income tax positions	[3]				0
AFUDC—Equity				25	36
Other				14	16
Other, net				43	54
Pepco Holdings LLC [Member] | Successor [Member]
Decommissioning-Related Activities [Abstract]
Investment income (loss)			$ 1
Long-term lease income			0
Interest income (expense) related to uncertain income tax positions			(1)
Benefit (penalty) related to uncertain income tax positions	[3]		0
AFUDC—Equity			23
Loss on debt extinguishment			0
Other			21
Other, net			$ 44
Pepco Holdings LLC [Member] | Predecessor [Member]
Decommissioning-Related Activities [Abstract]
Investment income (loss)		$ 0
Long-term lease income		0
Interest income (expense) related to uncertain income tax positions		0
Benefit (penalty) related to uncertain income tax positions	[3]	0
AFUDC—Equity		7
Loss on debt extinguishment		0
Other		(11)
Other, net		$ (4)
Potomac Electric Power Company [Member]
Decommissioning-Related Activities [Abstract]
Investment income (loss)				2	1	1
Long-term lease income						0
Interest income (expense) related to uncertain income tax positions				0	0	1
Benefit (penalty) related to uncertain income tax positions	[3]				0	0
AFUDC—Equity				22	23	19
Loss on debt extinguishment						0
Other				7	8	15
Other, net				31	32	36
Delmarva Power & Light Company [Member]
Decommissioning-Related Activities [Abstract]
Investment income (loss)				1	0	0
Long-term lease income						0
Interest income (expense) related to uncertain income tax positions				0	0	0
Benefit (penalty) related to uncertain income tax positions	[3]				0	0
AFUDC—Equity				2	7	5
Loss on debt extinguishment						0
Other				7	7	8
Other, net				10	14	13
Atlantic City Electric Company [Member]
Decommissioning-Related Activities [Abstract]
Investment income (loss)				0	0	1
Long-term lease income						0
Interest income (expense) related to uncertain income tax positions				0	0	0
Benefit (penalty) related to uncertain income tax positions	[3]				0	0
AFUDC—Equity				1	6	6
Loss on debt extinguishment						0
Other				1	1	2
Other, net				$ 2	$ 7	$ 9

[1] Includes investment income and realized gains and losses on sales of investments within the NDT funds.

[2] {F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOmVlYzRiNDIxOTkxNDRkN2ViNWYzYTRhOTVmMjFkNDYzfFRleHRTZWxlY3Rpb246MTE0OEY2QkJBNTBGNUFBQ0IwMkE4RTI0QzY3MTNDRUEM}

[3] See Note 14—Income Taxes for additional information on the penalty related to the Tax Court’s decision on Exelon’s like-kind exchange tax position.