Changes in Accumulated Other Comprehensive Income - Reclassification out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions		3 Months Ended			6 Months Ended
		Jun. 30, 2017	Jun. 30, 2016	Mar. 23, 2016	Jun. 30, 2017		Jun. 30, 2016
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income Tax Expense (Benefit)		$ (72)	$ 102		$ 143		$ 285
Net of tax / Total Reclassification for the period	[1]	(34)	(34)		(74)		(72)
Gains and (losses) on Cash Flow Hedges
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net of tax / Total Reclassification for the period					(4)		(3)	[2],[3]
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]
Total before tax		0
Income Tax Expense (Benefit)		0
Net of tax		0
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		46		38
Actuarial losses
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of pension and other postretirement benefit plan items	[1],[4]	(81)	(75)		(162)		(151)
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)	(56)		(116)		(113)
Tax benefit	[1]	(24)	(22)		(46)		(44)
Net of tax / Total Reclassification for the period	[1]	(34)	(34)		(70)	[2],[3]	(69)	[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]				(3)		(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		0			(7)	[1]	(5)	[1]
Total before tax	[1]				(7)		(5)
Income Tax Expense (Benefit)	[1]				3		2
Net of tax	[1]				(4)		(3)
Exelon Generation Co L L C [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income Tax Expense (Benefit)		(158)	(31)		(31)		120
Net of tax / Total Reclassification for the period	[1]	0	0		(4)		(3)
Exelon Generation Co L L C [Member] | Gains and (losses) on Cash Flow Hedges
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net of tax / Total Reclassification for the period					(4)		(3)	[2],[3]
Exelon Generation Co L L C [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]
Total before tax		0
Income Tax Expense (Benefit)		0
Net of tax		0
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
Net of tax / Total Reclassification for the period	[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		$ 0			(7)	[1]	(5)	[1]
Total before tax	[1]				(7)		(5)
Income Tax Expense (Benefit)	[1]				3		2
Net of tax	[1]				$ (4)		$ (3)
PEPCO Holdings Inc [Member] | Predecessor [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net of tax / Total Reclassification for the period	[1]			$ (1)
PEPCO Holdings Inc [Member] | Gains and (losses) on Cash Flow Hedges | Predecessor [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net of tax / Total Reclassification for the period	[2],[3]			0
PEPCO Holdings Inc [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 Inc [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 Inc [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
Net of tax / Total Reclassification for the period	[1],[2],[3]			(1)
PEPCO Holdings Inc [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 13 — Retirement Benefits for additional details).