Changes in Accumulated Other Comprehensive Income - Schedule of Changes in AOCI (Details) - USD ($) $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	$ 33,704	$ 33,070	$ 32,565	$ 32,187	$ 33,070	$ 32,187
Beginning Balance		30,764			30,764
Other comprehensive income	21		44		3	117
Ending balance	33,907	33,704	32,839	32,565	33,907	32,839
Ending Balance	31,548				31,548
Tax Cuts and Jobs Act, Reclassification from AOCI to Retained Earnings						539
Gains (Losses) on Cash Flow Hedges
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance		(2)		(14)	(2)	(14)
OCI before reclassifications					0	13
Amounts reclassified from AOCI					0	(1)
Other comprehensive income					0	12
Ending balance	(2)		(2)		(2)	(2)
Gains (Losses) on Cash Flow Hedges | Accounting Standards Update 2016-01 [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard(c)						0
Unrealized Gains (Losses) on Marketable Securities
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance				10		10
OCI before reclassifications						0
Amounts reclassified from AOCI						0
Other comprehensive income						0
Ending balance			0			0
Unrealized Gains (Losses) on Marketable Securities | Accounting Standards Update 2016-01 [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard(c)						(10)
Pension and Non-Pension Postretirement Benefit Plan Items
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance		(2,960)		(2,998)	(2,960)	(2,998)
OCI before reclassifications					(39)	20
Amounts reclassified from AOCI	20		44		42	88
Other comprehensive income					3	108
Ending balance	(2,957)		(2,890)		(2,957)	(2,890)
Pension and Non-Pension Postretirement Benefit Plan Items | Accounting Standards Update 2016-01 [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard(c)						0
Foreign Currency Items
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance		(33)		(23)	(33)	(23)
OCI before reclassifications					4	(6)
Amounts reclassified from AOCI					0	0
Other comprehensive income					4	(6)
Ending balance	(29)		(29)		(29)	(29)
Foreign Currency Items | Accounting Standards Update 2016-01 [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard(c)						0
AOCI of Investments in Unconsolidated Affiliates
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance		0		(1)	0	(1)
OCI before reclassifications					(2)	1
Amounts reclassified from AOCI					0	0
Other comprehensive income					(2)	1
Ending balance	(2)		0		(2)	0
AOCI of Investments in Unconsolidated Affiliates | Accounting Standards Update 2016-01 [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard(c)						0
Total
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	(3,012)	(2,995)	(2,965)	(3,026)	(2,995)	(3,026)
OCI before reclassifications					(37)	28
Amounts reclassified from AOCI					42	87
Other comprehensive income	22	(17)	44	71	5	115
Ending balance	(2,990)	(3,012)	(2,921)	(2,965)	(2,990)	(2,921)
Total | Accounting Standards Update 2016-01 [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard(c)						(10)
Exelon Generation Co L L C [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	15,696	15,508	15,958	15,959	15,508	15,959
Other comprehensive income	(1)	1	2	7	0	9
Ending Balance	15,592	15,696	15,939	15,958	15,592	15,939
Exelon Generation Co L L C [Member] | Gains (Losses) on Cash Flow Hedges
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance		(4)		(16)	(4)	(16)
OCI before reclassifications					0	13
Amounts reclassified from AOCI					0	(1)
Other comprehensive income					0	12
Ending Balance	(4)		(4)		(4)	(4)
Exelon Generation Co L L C [Member] | Gains (Losses) on Cash Flow Hedges | Accounting Standards Update 2016-01 [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard(c)						0
Exelon Generation Co L L C [Member] | Unrealized Gains (Losses) on Marketable Securities
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance				3		3
OCI before reclassifications						0
Amounts reclassified from AOCI						0
Other comprehensive income						0
Ending Balance			0			0
Exelon Generation Co L L C [Member] | Unrealized Gains (Losses) on Marketable Securities | Accounting Standards Update 2016-01 [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard(c)						(3)
Exelon Generation Co L L C [Member] | Pension and Non-Pension Postretirement Benefit Plan Items
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance		0		0	0	0
OCI before reclassifications					0	0
Amounts reclassified from AOCI					0	0
Other comprehensive income					0	0
Ending Balance	0		0		0	0
Exelon Generation Co L L C [Member] | Pension and Non-Pension Postretirement Benefit Plan Items | Accounting Standards Update 2016-01 [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard(c)						0
Exelon Generation Co L L C [Member] | Foreign Currency Items
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance		(33)		(23)	(33)	(23)
OCI before reclassifications					4	(6)
Amounts reclassified from AOCI					0	0
Other comprehensive income					4	(6)
Ending Balance	(29)		(29)		(29)	(29)
Exelon Generation Co L L C [Member] | Foreign Currency Items | Accounting Standards Update 2016-01 [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard(c)						0
Exelon Generation Co L L C [Member] | AOCI of Investments in Unconsolidated Affiliates
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance		(1)		(1)	(1)	(1)
OCI before reclassifications					(2)	1
Amounts reclassified from AOCI					0	0
Other comprehensive income					(2)	1
Ending Balance	(3)		0		(3)	0
Exelon Generation Co L L C [Member] | AOCI of Investments in Unconsolidated Affiliates | Accounting Standards Update 2016-01 [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard(c)						0
Exelon Generation Co L L C [Member] | Total
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	(36)	(38)	(34)	(37)	(38)	(37)
OCI before reclassifications					2	8
Amounts reclassified from AOCI					0	(1)
Other comprehensive income	0	2	1	6	2	7
Ending Balance	$ (36)	$ (36)	$ (33)	$ (34)	$ (36)	(33)
Exelon Generation Co L L C [Member] | Total | Accounting Standards Update 2016-01 [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard(c)						$ (3)