Changes in Accumulated Other Comprehensive Income Changes in Accumulated Other Comprehensive Income - Schedule of Changes in AOCI (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended		12 Months Ended
		Mar. 23, 2016		Dec. 31, 2016		Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance		$ 27,294				$ 27,612		$ 27,294		$ 24,133
Amounts reclassified from AOCI	[1]					144		150
Other comprehensive income (loss)						171		(36)		60
Ending Balance				$ 27,612		32,132		27,612		27,294
Exelon Generation Co L L C [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Amounts reclassified from AOCI	[1]					4		13
Other comprehensive income (loss)						15		9		(27)
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]					(1)		(6)
Amounts reclassified from AOCI	[2],[3]					4		8
Other comprehensive income (loss)	[2]					3		2
Ending Balance	[2]			(17)		(14)		(17)		(19)
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]					(1)		(6)
Amounts reclassified from AOCI	[2],[3]					4		8
Other comprehensive income (loss)	[2]					3		2
Ending Balance	[2]			(19)		(16)		(19)		(21)
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	[2],[3]					0		0
Other comprehensive income (loss)	[2]					0		0
Ending Balance	[2]			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)	[4]			(8)
OCI before reclassifications	[2]	0
Amounts reclassified from AOCI	[2],[3]	0
Other comprehensive income (loss)	[2]	0
Ending Balance	[2]	(8)	[4]							(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]					6		1
Amounts reclassified from AOCI	[2],[3]					0		0
Other comprehensive income (loss)	[2]					6		1
Ending Balance	[2]			4		10		4		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]					1		1
Amounts reclassified from AOCI	[2],[3]					0		0
Other comprehensive income (loss)	[2]					1		1
Ending Balance	[2]			2		3		2		1
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	[2],[3]					0		0
Other comprehensive income (loss)	[2]					0		0
Ending Balance	[2]			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	[4]			0
OCI before reclassifications	[2]	0
Amounts reclassified from AOCI	[2],[3]	0
Other comprehensive income (loss)	[2]	0
Ending Balance	[2]	0	[4]							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]					11		(182)
Amounts reclassified from AOCI	[1],[2],[3]					140		137
Other comprehensive income (loss)	[2]					151		(45)
Ending Balance	[2]			(2,610)		(2,459)		(2,610)		(2,565)
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	[1],[2],[3]					0		0
Other comprehensive income (loss)	[2]					0		0
Ending Balance	[2]			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	[2],[3]					0		0
Other comprehensive income (loss)	[2]					0		0
Ending Balance	[2]			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)	[4]			(28)
OCI before reclassifications	[2]	0
Amounts reclassified from AOCI	[2],[3]	1
Other comprehensive income (loss)	[2]	1
Ending Balance	[2]	(27)	[4]							(28)
Foreign Currency Items
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	[2]	(40)				(30)		(40)
OCI before reclassifications	[2]					7		5
Amounts reclassified from AOCI	[2],[3]					0		5
Other comprehensive income (loss)	[2]					7		10
Ending Balance	[2]			(30)		(23)		(30)		(40)
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		5
Amounts reclassified from AOCI	[2],[3]					0		5
Other comprehensive income (loss)	[2]					7		10
Ending Balance	[2]			(30)		(23)		(30)		(40)
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	[2],[3]					0		0
Other comprehensive income (loss)	[2]					0		0
Ending Balance	[2]			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	[4]			0
OCI before reclassifications	[2]	0
Amounts reclassified from AOCI	[2],[3]	0
Other comprehensive income (loss)	[2]	0
Ending Balance	[2]	0	[4]							0
AOCI of Equity Investments
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	[2]	(3)				(7)		(3)
OCI before reclassifications	[2]					6		(4)
Amounts reclassified from AOCI	[2],[3]					0		0
Other comprehensive income (loss)	[2]					6		(4)
Ending Balance	[2]			(7)		(1)		(7)		(3)
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		(4)
Amounts reclassified from AOCI	[2],[3]					0		0
Other comprehensive income (loss)	[2]					6		(4)
Ending Balance	[2]			(7)		(1)		(7)		(3)
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	[2],[3]					0		0
Other comprehensive income (loss)	[2]					0		0
Ending Balance	[2]			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	[4]			0
OCI before reclassifications	[2]	0
Amounts reclassified from AOCI	[2],[3]	0
Other comprehensive income (loss)	[2]	0
Ending Balance	[2]	0	[4]							0
Total
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance		(2,624)	[2]			(2,660)	[2]	(2,624)	[2]	(2,684)
OCI before reclassifications	[2]					29		(186)
Amounts reclassified from AOCI	[2],[3]					144		150
Other comprehensive income (loss)						173	[2]	(36)	[2]	60
Ending Balance	[2]			(2,660)		(2,487)		(2,660)		(2,624)
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]					13		(4)
Amounts reclassified from AOCI	[2],[3]					4		13
Other comprehensive income (loss)						17	[2]	9	[2]	(27)
Ending Balance	[2]			(54)		(37)		(54)		(63)
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	[2],[3]					0		0
Other comprehensive income (loss)	[2]					0		0
Ending Balance	[2]			1		$ 1		1		1
Total | PEPCO Holdings Inc [Member] | Predecessor [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	[2]	(36)		$ (35)	[4]			$ (36)
OCI before reclassifications	[2]	0
Amounts reclassified from AOCI	[2],[3]	1
Other comprehensive income (loss)	[2]	1
Ending Balance	[2]	$ (35)	[4]							$ (36)

[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.

[4] 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.