Fair Value of Financial Assets and Liabilities - Fair Value Assets and Liabilities Measure on Recurring Basis Gain Loss Included in Earnings (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating Revenue [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings		$ 67	$ 614
Included in other comprehensive income		858	663
Purchased Fuel and Electric [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings		(45)	(88)
Included in other comprehensive income		(2)	(23)
Other, net [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings		4	6
Included in other comprehensive income		4	4
Exelon Generation Co L L C [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Assets and Liabilities Measured on Recurring Basis, Gain (Loss) Included in Earnings		(834)	(114)
Exelon Generation Co L L C [Member] | Operating Revenue [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings		67	614
Included in other comprehensive income		858	663
Exelon Generation Co L L C [Member] | Purchased Fuel and Electric [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings		(45)	(88)
Included in other comprehensive income		(2)	(23)
Exelon Generation Co L L C [Member] | Other, net [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings		4	6
Included in other comprehensive income		4	4
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value		(1,794)	(1,721)	$ (749)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales		$ (108)	$ (80)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings, Description		27	532
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Noncurrent Payables To Affiliates		$ 0	$ 0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Included In Nuclear Decommissioning Payable		(2)	2
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Included In Regulatory Assets Liabilities		(17)	0
Change in collateral		29	198
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases		420	598
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements		(106)	(64)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3		84	(7)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3		(254)	(207)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Total Gain Loss Included In Earnings Attributed To Changes In Unrealized Gains Losses		860	644
Fair Value, Inputs, Level 3 [Member] | Exelon Generation Co L L C [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value		(2,041)	(1,928)	(942)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales		(108)	(80)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements		$ (106)	(64)
Included in other comprehensive income			$ 0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings, Description		27	532
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Noncurrent Payables To Affiliates		$ 23	$ 14
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Included In Nuclear Decommissioning Payable		(2)	2
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Included In Regulatory Assets Liabilities		0	0
Change in collateral		29	198
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases		420	598
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3		84	(7)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3		(254)	(207)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Total Gain Loss Included In Earnings Attributed To Changes In Unrealized Gains Losses		860	644
Other Investments [Member] | Fair Value, Inputs, Level 3 [Member] | Exelon Generation Co L L C [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value		(33)	(3)	(15)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales		$ 0	(8)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements			$ 0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings, Description		1	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Noncurrent Payables To Affiliates		$ 0	$ 0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Included In Nuclear Decommissioning Payable		0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Included In Regulatory Assets Liabilities		0	0
Change in collateral		0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases		30	2
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3		0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3		(1)	(6)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Total Gain Loss Included In Earnings Attributed To Changes In Unrealized Gains Losses		0	0
Nuclear Decommissioning Trust Fund Investments [Member] | Fair Value, Inputs, Level 3 [Member] | Exelon Generation Co L L C [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value		(830)	(691)	(350)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales		$ (8)	(15)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements			$ (64)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings, Description		4	6
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Noncurrent Payables To Affiliates		$ 23	$ 14
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Included In Nuclear Decommissioning Payable		0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Included In Regulatory Assets Liabilities		0	0
Change in collateral		0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases		226	400
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements		(106)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3		4	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3		(4)	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Total Gain Loss Included In Earnings Attributed To Changes In Unrealized Gains Losses		4	4
Derivative [Member] | Fair Value, Inputs, Level 3 [Member] | Exelon Generation Co L L C [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value		(1,051)	(1,050)	(465)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales		$ (25)	$ (7)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings, Description		22	526
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Noncurrent Payables To Affiliates		$ 0	$ 0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Included In Nuclear Decommissioning Payable		0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Included In Regulatory Assets Liabilities		0	0
Change in collateral		29	198
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases		144	76
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements		0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3		80	(7)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3		(249)	(201)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Total Gain Loss Included In Earnings Attributed To Changes In Unrealized Gains Losses		856	640
Derivative [Member] | Fair Value, Inputs, Level 3 [Member] | Commonwealth Edison Co [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value			(207)	(193)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales		$ 0	$ 0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings, Description		0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Noncurrent Payables To Affiliates		$ 0	$ 0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Included In Nuclear Decommissioning Payable		0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Included In Regulatory Assets Liabilities		(40)	(14)
Change in collateral		0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases		0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements		0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3		0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3		0	0
Fair Value, Measurement with Unobservable Inputs Reconciliations, Recurring Basis, Liability Value		(247)	(207)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Total Gain Loss Included In Earnings Attributed To Changes In Unrealized Gains Losses		0	0
Pledged Assets For Zion Station Decommissioning [Member] | Fair Value, Inputs, Level 3 [Member] | Exelon Generation Co L L C [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value		(127)	(184)	(112)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales		$ (75)	(50)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements			$ 0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings, Description		0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Noncurrent Payables To Affiliates		$ 0	$ 0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Included In Nuclear Decommissioning Payable		(2)	2
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Included In Regulatory Assets Liabilities		0	0
Change in collateral		0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases		20	120
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3		0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3		0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Total Gain Loss Included In Earnings Attributed To Changes In Unrealized Gains Losses		0	0
Derivative [Member] | Fair Value, Inputs, Level 3 [Member] | Exelon Generation Co L L C [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Included in other comprehensive income	[1]		0
Derivative [Member] | Fair Value, Inputs, Level 3 [Member] | Consolidation, Eliminations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value		0	0	$ 0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales		$ 0	$ 0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings, Description		0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Noncurrent Payables To Affiliates		$ (23)	$ (14)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Included In Nuclear Decommissioning Payable		0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Included In Regulatory Assets Liabilities		23	14
Change in collateral		0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases		0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements		0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3		0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3		0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Total Gain Loss Included In Earnings Attributed To Changes In Unrealized Gains Losses		0	0
Interest Rate Swap [Member] | Exelon Generation Co L L C [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements		$ (15)	$ (1)

[1] Includes $55 million of decreases in fair value and an increase for realized losses due to settlements of $(15) million recorded in purchased power expense associated with floating-to-fixed energy swap contracts with unaffiliated suppliers for the year ended December 31, 2015. Includes $13 million of decreases in fair value and a reduction for realized gains due to settlements of $1 million for the year ended December 31, 2014.