Segment Information - Generation Total Revenues (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018
Segment Reporting Information [Line Items]
Revenues		$ 9,477	$ 9,693
Operating revenues from affiliates	[1]	0	0
Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenues		1,256	1,440
Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues		1,108	1,346
Generation New York [Member]
Segment Reporting Information [Line Items]
Revenues		393	409
Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenues		212	209
Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenues		1,353	1,080
Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenues		4,322	4,484
Generation Natural Gas [Member]
Segment Reporting Information [Line Items]
Revenues		894	980
Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues	[2]	80	48
Unrealized Gain (Loss) on Securities		(52)	(98)
Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenues		5,296	5,512
Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	[3]	9,477	9,693
Operating Segments [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenues	[4]	1,262	1,435
Operating Segments [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues	[4]	1,114	1,344
Operating Segments [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Revenues	[4]	393	410
Operating Segments [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenues	[4]	209	208
Operating Segments [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenues	[4]	1,359	1,112
Operating Segments [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenues	[4]	4,337	4,509
Operating Segments [Member] | Generation Natural Gas [Member]
Segment Reporting Information [Line Items]
Revenues	[4]	879	955
Operating Segments [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Unrealized Gain (Loss) on Securities		(28)	(266)
Operating Segments [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenues	[4]	5,296	5,512
Corporate, Non-Segment [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues	[4],[5]	80	48
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	[3]	(786)	(876)
Operating revenues from affiliates	[1]	(785)	(876)
Intersegment Eliminations [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		(6)	5
Intersegment Eliminations [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		(6)	2
Intersegment Eliminations [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		0	(1)
Intersegment Eliminations [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		3	1
Intersegment Eliminations [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		(6)	(32)
Intersegment Eliminations [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		(15)	(25)
Intersegment Eliminations [Member] | Generation Natural Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		15	25
Intersegment Eliminations [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[2]	0	0
Intersegment Eliminations [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		0	0
Revenue from Contract with Customer [Member] | Operating Segments [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenues	[4]	1,286	1,355
Revenue from Contract with Customer [Member] | Operating Segments [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues	[4]	1,055	1,273
Revenue from Contract with Customer [Member] | Operating Segments [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Revenues	[4]	409	439
Revenue from Contract with Customer [Member] | Operating Segments [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenues	[4]	130	149
Revenue from Contract with Customer [Member] | Operating Segments [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenues	[4]	1,165	935
Revenue from Contract with Customer [Member] | Operating Segments [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenues	[4]	4,045	4,151
Revenue from Contract with Customer [Member] | Operating Segments [Member] | Generation Natural Gas [Member]
Segment Reporting Information [Line Items]
Revenues	[4]	584	522
Revenue from Contract with Customer [Member] | Operating Segments [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenues	[4]	4,749	4,807
Revenue from Contract with Customer [Member] | Corporate, Non-Segment [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues	[4],[5]	120	134
Other [Member] | Operating Segments [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenues	[4],[6]	(24)	80
Other [Member] | Operating Segments [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues	[4],[6]	59	71
Other [Member] | Operating Segments [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Revenues	[4],[6]	(16)	(29)
Other [Member] | Operating Segments [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenues	[4],[6]	79	59
Other [Member] | Operating Segments [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenues	[4],[6]	194	177
Other [Member] | Operating Segments [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenues	[4],[6]	292	358
Other [Member] | Operating Segments [Member] | Generation Natural Gas [Member]
Segment Reporting Information [Line Items]
Revenues	[4],[6]	295	433
Other [Member] | Operating Segments [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenues	[4],[6]	547	705
Other [Member] | Corporate, Non-Segment [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues	[4],[5],[6]	$ (40)	$ (86)

[1] Intersegment revenues exclude sales to unconsolidated affiliates. The intersegment profit associated with Generation’s sale of certain products and services by and between Exelon’s segments is not eliminated in consolidation due to the recognition of intersegment profit in accordance with regulatory accounting guidance. For Exelon, these amounts are included in Operating revenues in the Consolidated Statements of Operations and Comprehensive Income.

[2] {F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOjhiOGQyMzgxMWZiYjQ2YjNiZDRmMDg0ZmFhZDBiZGFjfFRleHRTZWxlY3Rpb246Nzg0RjkwRDlGOTIxNTBDQkFGM0EzREE2MkIyMjdEOTEM}

[3] Includes gross utility tax receipts from customers. The offsetting remittance of utility taxes to the governing bodies is recorded in expenses in the Registrants’ Consolidated Statements of Operations and Comprehensive Income. See Note 17 — Supplemental Financial Information for additional information on total utility taxes.

[4] des all wholesale and retail electric sales to third parties and affiliated sales to the Utility Registrants.(b)

[5] represents activities not allocated to a region. See text above for a description of included activities. Includes unrealized mark-to-market losses of $52 million and $98 million in 2019 and 2018, respectively, and elimination of intersegment revenues.Reve

[6] des revenues from derivatives and leases. (c)