Changes in Accumulated Other Comprehensive Income - Reclassification out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions		3 Months Ended			9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Mar. 23, 2016	Sep. 30, 2017		Sep. 30, 2016
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other, net		$ 237	$ 120		$ 725		$ 377
Income Tax Expense (Benefit)		452	340		595		625
Amounts reclassified from AOCI	[1]	(34)	(42)		(108)		(114)
Net income		867	526		1,911		956
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other, net	[1]		(5)				(5)
Total before tax	[1]		(5)				(5)
Income Tax Expense (Benefit)	[1]		0				0
Net income	[1]		(5)				(5)
Gains and (losses) on Cash Flow Hedges
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amounts reclassified from AOCI	[2],[3]				(3)		(5)
Prior service costs
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of pension and other postretirement benefit plan items	[1],[4]	23	19		69		57
Actuarial losses
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of pension and other postretirement benefit plan items	[1],[4]	(81)	(76)		(243)		(227)
Pension and Non-Pension Postretirement Benefit Plan Items
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of pension and other postretirement benefit plan items	[1]	(58)	(57)		(174)		(170)
Tax benefit	[1]	23	22		69		66
Amounts reclassified from AOCI	[1]	(35)	(35)		(105)	[2],[3]	(104)	[2],[3]
Cash Flow Hedging [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income Tax Expense (Benefit)		1			(2)		(2)
Cash Flow Hedging [Member] | Gains and (losses) on Cash Flow Hedges | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other cash flow hedges	[1]	2	(3)		(5)		(8)
Total before tax	[1]	2	(3)		(5)		(8)
Income Tax Expense (Benefit)	[1]	(1)	1		2		3
Net of tax	[1]	1	(2)		(3)		(5)
Exelon Generation Co L L C [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other, net		209	185		648		395
Income Tax Expense (Benefit)		240	173		209		293
Amounts reclassified from AOCI	[1]	1	(7)		(3)		(10)
Net income		348	271		491		556
Exelon Generation Co L L C [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other, net	[1]		(5)				(5)
Total before tax	[1]		(5)				(5)
Income Tax Expense (Benefit)	[1]		0				0
Net income	[1]		(5)				(5)
Exelon Generation Co L L C [Member] | Gains and (losses) on Cash Flow Hedges
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amounts reclassified from AOCI	[2],[3]				(3)	[5]	(5)
Exelon Generation Co L L C [Member] | Prior service costs
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of pension and other postretirement benefit plan items	[1],[4]	0	0		0		0
Exelon Generation Co L L C [Member] | Actuarial losses
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of pension and other postretirement benefit plan items	[1],[4]	0	0		0		0
Exelon Generation Co L L C [Member] | Pension and Non-Pension Postretirement Benefit Plan Items
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of pension and other postretirement benefit plan items	[1]	0	0		0		0
Tax benefit	[1]	0	0		0		0
Amounts reclassified from AOCI	[1]	0	0		0	[2],[3]	0	[2],[3]
Exelon Generation Co L L C [Member] | Cash Flow Hedging [Member] | Gains and (losses) on Cash Flow Hedges | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other cash flow hedges	[1]	2	(3)		(5)		(8)
Total before tax	[1]	2	(3)		(5)		(8)
Income Tax Expense (Benefit)	[1]	(1)	1		2		3
Net of tax	[1]	$ 1	$ (2)		$ (3)		$ (5)
Pepco Holdings LLC [Member] | Predecessor [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other, net				$ (4)
Income Tax Expense (Benefit)				17
Amounts reclassified from AOCI	[1]			(1)
Net income				19
Pepco Holdings LLC [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Predecessor [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other, net	[1]			0
Total before tax	[1]			0
Income Tax Expense (Benefit)	[1]			0
Net income	[1]			0
Pepco Holdings LLC [Member] | Prior service costs | Predecessor [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of pension and other postretirement benefit plan items	[1],[4]			0
Pepco Holdings LLC [Member] | Actuarial losses | Predecessor [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of pension and other postretirement benefit plan items	[1],[4]			(1)
Pepco Holdings LLC [Member] | Pension and Non-Pension Postretirement Benefit Plan Items | Predecessor [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of pension and other postretirement benefit plan items	[1]			(1)
Tax benefit	[1]			0
Amounts reclassified from AOCI	[1]			(1)
Pepco Holdings LLC [Member] | Cash Flow Hedging [Member] | Gains and (losses) on Cash Flow Hedges | Reclassification out of Accumulated Other Comprehensive Income [Member] | Predecessor [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other cash flow hedges	[1]			0
Total before tax	[1]			0
Income Tax Expense (Benefit)	[1]			0
Net of tax	[1]			$ 0

[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] This AOCI component is included in the computation of net periodic pension and OPEB cost (see Note 14 — Retirement Benefits for additional details).

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