Changes in Accumulated Other Comprehensive Income - Schedule of Changes in AOCI (Details) - USD ($) $ in Millions		3 Months Ended			6 Months Ended		9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Mar. 23, 2016	Sep. 30, 2016		Sep. 30, 2017		Sep. 30, 2016
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance							$ 27,612
Amounts reclassified from AOCI(b)	[1]	$ 34	$ 42				108		$ 114
Other comprehensive income		44	36				69		96
Ending balance		30,317					30,317
Exelon Generation Co L L C [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Amounts reclassified from AOCI(b)	[1]	(1)	7				3		10
Other comprehensive income		4	4				16		2
Gains and (losses) on Cash Flow Hedges
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[2]			$ (19)			(17)		(19)
OCI before reclassifications	[2]						2		(9)
Amounts reclassified from AOCI(b)	[2],[3]						3		5
Other comprehensive income	[2]						5		(4)
Ending balance	[2]	(12)	(23)		$ (23)		(12)		(23)
Gains and (losses) on Cash Flow Hedges | Exelon Generation Co L L C [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[2]			(21)			(19)		(21)
OCI before reclassifications	[2]						2		(8)
Amounts reclassified from AOCI(b)	[2],[3]						3	[4]	5
Other comprehensive income	[2]						5		(3)
Ending balance	[2]	(14)	(24)		(24)		(14)		(24)
Gains and (losses) on Cash Flow Hedges | PECO Energy Co [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[2]			0			0		0
OCI before reclassifications	[2]						0		0
Amounts reclassified from AOCI(b)	[2],[3]						0		0
Other comprehensive income	[2]						0		0
Ending balance	[2]	0	0		0		0		0
Gains and (losses) on Cash Flow Hedges | PEPCO Holdings Inc [Member] | Predecessor [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[2]			(8)	(8)	[5]			(8)
OCI before reclassifications	[2]			0
Amounts reclassified from AOCI(b)	[2],[3]			0
Other comprehensive income	[2]			0
Ending balance	[2],[5]			(8)
Unrealized Gains and (losses) on Marketable Securities
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[2]			3			4		3
OCI before reclassifications	[2]						2		0
Amounts reclassified from AOCI(b)	[2],[3]						0		0
Other comprehensive income	[2]						2		0
Ending balance	[2]	6	3		3		6		3
Unrealized Gains and (losses) on Marketable Securities | Exelon Generation Co L L C [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[2]			1			2		1
OCI before reclassifications	[2]						0		1
Amounts reclassified from AOCI(b)	[2],[3]						0		0
Other comprehensive income	[2]						0		1
Ending balance	[2]	2	2		2		2		2
Unrealized Gains and (losses) on Marketable Securities | PECO Energy Co [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[2]			1			1		1
OCI before reclassifications	[2]						0		0
Amounts reclassified from AOCI(b)	[2],[3]						0		0
Other comprehensive income	[2]						0		0
Ending balance	[2]	1	1		1		1		1
Unrealized Gains and (losses) on Marketable Securities | PEPCO Holdings Inc [Member] | Predecessor [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[2]			0	0	[5]			0
OCI before reclassifications	[2]			0
Amounts reclassified from AOCI(b)	[2],[3]			0
Other comprehensive income	[2]			0
Ending balance	[2],[5]			0
Pension and Non-Pension Postretirement Benefit Plan Items
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[2]			(2,565)			(2,610)		(2,565)
OCI before reclassifications	[2]						(55)		(2)
Amounts reclassified from AOCI(b)	[1]	35	35				105	[2],[3]	104	[2],[3]
Other comprehensive income	[2]						50		102
Ending balance	[2]	(2,560)	(2,463)		(2,463)		(2,560)		(2,463)
Pension and Non-Pension Postretirement Benefit Plan Items | Exelon Generation Co L L C [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[2]			0			0		0
OCI before reclassifications	[2]						0		0
Amounts reclassified from AOCI(b)	[1]	0	0				0	[2],[3]	0	[2],[3]
Other comprehensive income	[2]						0		0
Ending balance	[2]	0	0		0		0		0
Pension and Non-Pension Postretirement Benefit Plan Items | PECO Energy Co [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[2]			0			0		0
OCI before reclassifications	[2]						0		0
Amounts reclassified from AOCI(b)	[2],[3]						0		0
Other comprehensive income	[2]						0		0
Ending balance	[2]	0	0		0		0		0
Pension and Non-Pension Postretirement Benefit Plan Items | PEPCO Holdings Inc [Member] | Predecessor [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[2]			(28)	(27)	[5]			(28)
OCI before reclassifications	[2]			0
Amounts reclassified from AOCI(b)	[2],[3]			1
Other comprehensive income	[2]			1
Ending balance	[2],[5]			(27)
Foreign Currency Items
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[2]			(40)			(30)		(40)
OCI before reclassifications	[2]						7		3
Amounts reclassified from AOCI(b)	[2],[3]						0		5
Other comprehensive income	[2]						7		8
Ending balance	[2]	(23)	(32)		(32)		(23)		(32)
Foreign Currency Items | Exelon Generation Co L L C [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[2]			(40)			(30)		(40)
OCI before reclassifications	[2]						7		3
Amounts reclassified from AOCI(b)	[2],[3]						0		5
Other comprehensive income	[2]						7		8
Ending balance	[2]	(23)	(32)		(32)		(23)		(32)
Foreign Currency Items | PECO Energy Co [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[2]			0			0		0
OCI before reclassifications	[2]						0		0
Amounts reclassified from AOCI(b)	[2],[3]						0		0
Other comprehensive income	[2]						0		0
Ending balance	[2]	0	0		0		0		0
Foreign Currency Items | PEPCO Holdings Inc [Member] | Predecessor [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[2]			0	0	[5]			0
OCI before reclassifications	[2]			0
Amounts reclassified from AOCI(b)	[2],[3]			0
Other comprehensive income	[2]			0
Ending balance	[2],[5]			0
AOCI of Equity Investments
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[2]			(3)			(7)		(3)
OCI before reclassifications	[2]						7		(5)
Amounts reclassified from AOCI(b)	[2],[3]						0		0
Other comprehensive income	[2]						7		(5)
Ending balance	[2]	0	(8)		(8)		0		(8)
AOCI of Equity Investments | Exelon Generation Co L L C [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[2]			(3)			(7)		(3)
OCI before reclassifications	[2]						6		1
Amounts reclassified from AOCI(b)	[2],[3]						0		0
Other comprehensive income	[2]						6		1
Ending balance	[2]	(1)	(2)		(2)		(1)		(2)
AOCI of Equity Investments | PECO Energy Co [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[2]			0			0		0
OCI before reclassifications	[2]						0		0
Amounts reclassified from AOCI(b)	[2],[3]						0		0
Other comprehensive income	[2]						0		0
Ending balance	[2]	0	0		0		0		0
AOCI of Equity Investments | PEPCO Holdings Inc [Member] | Predecessor [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[2]			0	0	[5]			0
OCI before reclassifications	[2]			0
Amounts reclassified from AOCI(b)	[2],[3]			0
Other comprehensive income	[2]			0
Ending balance	[2],[5]			0
Total
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[2]			(2,624)			(2,660)		(2,624)
OCI before reclassifications	[2]						(37)		(13)
Amounts reclassified from AOCI(b)	[2],[3]						108		114
Other comprehensive income	[2]						71		101
Ending balance	[2]	(2,589)	(2,523)		(2,523)		(2,589)		(2,523)
Total | Exelon Generation Co L L C [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[2]			(63)			(54)		(63)
OCI before reclassifications	[2]						15		(3)
Amounts reclassified from AOCI(b)	[2],[3]						3		10
Other comprehensive income	[2]						18		7
Ending balance	[2]	(36)	(56)		(56)		(36)		(56)
Total | PECO Energy Co [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[2]			1			1		1
OCI before reclassifications	[2]						0		0
Amounts reclassified from AOCI(b)	[2],[3]						0		0
Other comprehensive income	[2]						0		0
Ending balance	[2]	$ 1	$ 1		1		$ 1		1
Total | PEPCO Holdings Inc [Member] | Predecessor [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[2]			(36)	$ (35)	[5]			$ (36)
OCI before reclassifications	[2]			0
Amounts reclassified from AOCI(b)	[2],[3]			1
Other comprehensive income	[2]			1
Ending balance	[2],[5]			$ (35)

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

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

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

[4] Amount is net of related income tax expense of $2 million for the nine months ended September 30, 2017.

[5] As a result of the PHI Merger, the PHI predecessor balances at March 23, 2016 were reduced to zero on March 24, 2016 due to purchase accounting adjustments applied to PHI.