Changes in Accumulated Other Comprehensive Income - Reclassification out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income Tax Expense (Benefit)		$ 59	$ 211
Amortization of pension and other postretirement benefit plan items		4
Amounts reclassified from AOCI		(44)	(40)
Gains and (losses) on Cash Flow Hedges
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amounts reclassified from AOCI	[1],[2]	0	(4)
Prior service costs
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of pension and other postretirement benefit plan items	[3],[4]	23	23
Actuarial losses
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of pension and other postretirement benefit plan items	[3],[4]	(83)	(81)
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	[3]	(60)	(58)
Tax benefit	[3]	16	22
Amounts reclassified from AOCI	[1],[2],[3]	(44)	(36)
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)			3
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	[3]		(7)
Total before tax	[3]		(7)
Income Tax Expense (Benefit)	[3]		3
Net of tax	[3]		(4)
Exelon Generation Co L L C [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income Tax Expense (Benefit)		9	123
Amortization of pension and other postretirement benefit plan items		3
Amounts reclassified from AOCI			(4)
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	[1],[2]	0	(4)
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	[3],[4]		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	[3],[4]		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	[3]		0
Tax benefit	[3]		0
Amounts reclassified from AOCI	[1],[2]	$ 0	0	[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	[3]		(7)
Total before tax	[3]		(7)
Income Tax Expense (Benefit)	[3]		3
Net of tax	[3]		$ (4)

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

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

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

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