Changes in Accumulated Other Comprehensive Income - Schedule of Changes in AOCI (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance		$ 33,070	$ 32,187
Beginning Balance		30,764
Amounts reclassified from AOCI	[1]	20	44
Other comprehensive (loss) income		(18)	72
Ending balance		33,704	32,565
Ending Balance		31,357
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]	(2)	(14)
OCI before reclassifications	[2]	0	8
Amounts reclassified from AOCI	[2],[3]	0	0
Other comprehensive (loss) income	[2]	0	8
Ending balance	[2]	(2)	(6)
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	[2]	0	10
OCI before reclassifications	[2]	0	0
Amounts reclassified from AOCI	[2],[3]	0	0
Other comprehensive (loss) income	[2]	0	0
Ending balance	[2]	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]	(2,960)	(2,998)
OCI before reclassifications	[2]	(38)	18
Amounts reclassified from AOCI	[1],[2],[3]	20	44
Other comprehensive (loss) income	[2]	(18)	62
Ending balance	[2]	(2,978)	(2,936)
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	[2]	(33)	(23)
OCI before reclassifications	[2]	2	1
Amounts reclassified from AOCI	[2],[3]	0	0
Other comprehensive (loss) income	[2]	2	1
Ending balance	[2]	(31)	(22)
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	[2]	0	(1)
OCI before reclassifications	[2]	(1)	0
Amounts reclassified from AOCI	[2],[3]	0	0
Other comprehensive (loss) income	[2]	(1)	0
Ending balance	[2]	(1)	(1)
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	[2]	(2,995)	(3,026)
OCI before reclassifications	[2]	(37)	27
Amounts reclassified from AOCI	[2],[3]	20	44
Other comprehensive (loss) income	[2]	(17)	71
Ending balance	[2]	(3,012)	(2,965)
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		15,508	15,959
Other comprehensive (loss) income		1	7
Ending Balance		15,696	15,958
Exelon Generation Co L L C [Member] | Gains (Losses) on Cash Flow Hedges
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	[2]	(4)	(16)
OCI before reclassifications	[2]	0	7
Amounts reclassified from AOCI	[2],[3]	1	0
Other comprehensive (loss) income	[2]	1	7
Ending Balance	[2]	(3)	(9)
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	[2]	0	3
OCI before reclassifications	[2]	0	0
Amounts reclassified from AOCI	[2],[3]	0	0
Other comprehensive (loss) income	[2]	0	0
Ending Balance	[2]	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	[2]	0	0
OCI before reclassifications	[2]	0	0
Amounts reclassified from AOCI	[2],[3]	0	0
Other comprehensive (loss) income	[2]	0	0
Ending Balance	[2]	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	[2]	(33)	(23)
OCI before reclassifications	[2]	2	(1)
Amounts reclassified from AOCI	[2],[3]	0	0
Other comprehensive (loss) income	[2]	2	(1)
Ending Balance	[2]	(31)	(24)
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	[2]	(1)	(1)
OCI before reclassifications	[2]	(1)	0
Amounts reclassified from AOCI	[2],[3]	0	0
Other comprehensive (loss) income	[2]	(1)	0
Ending Balance	[2]	(2)	(1)
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	[2]	(38)	(37)
OCI before reclassifications	[2]	1	6
Amounts reclassified from AOCI	[2],[3]	1	0
Other comprehensive (loss) income	[2]	2	6
Ending Balance	[2]	$ (36)	(34)
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)

[1] Amounts in parenthesis represent a decrease in net income.

[2] All amounts are net of tax and noncontrolling interests. Amounts in parenthesis represent a decrease in AOCI.

[3] See next tables for details about these reclassifications.