Fair Value of Financial Assets and Liabilities - Fair Value Reconciliation of Level 3 Assets and Liabilities Measured on a Recurring Basis (Details) - USD ($) $ in Millions		3 Months Ended	9 Months Ended		12 Months Ended
		Mar. 23, 2016	Dec. 31, 2016		Dec. 31, 2016		Dec. 31, 2015	Mar. 24, 2016	Dec. 31, 2014
Exelon Generation Co L L C [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Assets and Liabilities Measured on Recurring Basis, Gain (Loss) Included in Earnings					$ 677		$ 834
Fair Value Measurement With Unobservable inputs reconciliation Recurring Asset Liability Gain Loss Abstract [Abstract]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements					18		(15)
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)					116		858
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 Value			$ 993		$ 993		$ 1,529		$ 1,501
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings, Description					-557		27
Fair Value Measurement With Unobservable inputs reconciliation Recurring Asset Liability Gain Loss Abstract [Abstract]
Change in collateral					$ (141)		$ 29
Purchases					494		322
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements					(144)		(95)
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Included in payable for Zion Station decommissioning							(2)
Included in regulatory assets/liabilities					5		(22)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales					(15)		(61)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3					2		84
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3					(197)		(254)
Fair Value, Inputs, Level 3 [Member] | 6311 Life Insurance [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Issuances					(3)
Fair Value, Inputs, Level 3 [Member] | Derivative [Member] | Consolidation, Eliminations [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)					0		0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Noncurrent Payables To Affiliates					(16)		(18)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value			0		$ 0		$ 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 Asset Liability Gain Loss Abstract [Abstract]
Change in collateral					$ 0		$ 0
Purchases					0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements					0		0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Included in payable for Zion Station decommissioning							0
Included in regulatory assets/liabilities					16		18
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales					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, Inputs, Level 3 [Member] | Potomac Electric Power Company [Member] | 6311 Life Insurance [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value			19		$ 19		$ 19		18
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings, Description					3		5
Fair Value Measurement With Unobservable inputs reconciliation Recurring Asset Liability Gain Loss Abstract [Abstract]
Purchases					$ (3)		$ (3)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements					0		1
The amount of total gains (losses) included in income attributed to the change in unrealized gains (losses) related to assets and liabilities					3		3
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases, (Sales), Issuances, (Settlements) [Abstract]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Total Gain Loss Included In Earnings Attributed To Changes In Unrealized Gains Losses					3		3
Fair Value, Inputs, Level 3 [Member] | Delmarva Power and Light Company [Member] | 6311 Life Insurance [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value			0		$ 0		$ 0		1
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 Asset Liability Gain Loss Abstract [Abstract]
Purchases					$ 0		$ 0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements					0		1
The amount of total gains (losses) included in income attributed to the change in unrealized gains (losses) related to assets and liabilities					0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases, (Sales), Issuances, (Settlements) [Abstract]
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
Fair Value, Inputs, Level 3 [Member] | Exelon Generation Co L L C [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)					114		858
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Noncurrent Payables To Affiliates					16		18
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value			1,231		$ 1,231		$ 1,776		1,708
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings, Description					-560		27
Fair Value Measurement With Unobservable inputs reconciliation Recurring Asset Liability Gain Loss Abstract [Abstract]
Change in collateral					$ (141)		$ 29
Purchases					494		322
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements					(144)		(95)
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Period Increase (Decrease)					29		55
Included in payable for Zion Station decommissioning							(2)
Included in regulatory assets/liabilities					0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales					(15)		(61)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3					2		84
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3					(197)		(254)
Fair Value, Inputs, Level 3 [Member] | Exelon Generation Co L L C [Member] | Nuclear Decommissioning Trust Fund Investments [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)					5		2
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Noncurrent Payables To Affiliates					16		18
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value			677		$ 677		$ 670		605
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings, Description					7		4
Fair Value Measurement With Unobservable inputs reconciliation Recurring Asset Liability Gain Loss Abstract [Abstract]
Change in collateral					$ 0		$ 0
Purchases					143		146
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements					(144)		(95)
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Included in payable for Zion Station decommissioning							0
Included in regulatory assets/liabilities					0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales					(1)		(8)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3					0		4
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3					(14)		(4)
Fair Value, Inputs, Level 3 [Member] | Exelon Generation Co L L C [Member] | Pledged Assets For Zion Station Decommissioning [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)					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 Value			19		$ 19		$ 22		50
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 Asset Liability Gain Loss Abstract [Abstract]
Change in collateral					$ 0		$ 0
Purchases					2		2
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements					0		0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Included in payable for Zion Station decommissioning							(2)
Included in regulatory assets/liabilities					0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales					(5)		(28)
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, Inputs, Level 3 [Member] | Exelon Generation Co L L C [Member] | Derivative [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)					109		856
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 Value			493		$ 493		$ 1,051		1,050
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings, Description	[1]				-568		22
Fair Value Measurement With Unobservable inputs reconciliation Recurring Asset Liability Gain Loss Abstract [Abstract]
Change in collateral					$ (141)		$ 29
Purchases					342	[2]	144
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements					0		0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Included in payable for Zion Station decommissioning							0
Included in regulatory assets/liabilities					0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales					(9)		(25)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3					1		80
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3					(183)		(249)
Indefinite-lived Intangible Assets Acquired					168
Fair Value, Inputs, Level 3 [Member] | Exelon Generation Co L L C [Member] | Other Investments [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)					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 Value			42		$ 42		$ 33		3
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings, Description					1		1
Fair Value Measurement With Unobservable inputs reconciliation Recurring Asset Liability Gain Loss Abstract [Abstract]
Change in collateral					$ 0		$ 0
Purchases					7		30
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements					0		0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Included in payable for Zion Station decommissioning							0
Included in regulatory assets/liabilities					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 Transfers Into Level 3					1		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3					0		(1)
Fair Value, Inputs, Level 3 [Member] | Commonwealth Edison Co [Member] | Derivative [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	[3]				0		0
Fair Value, Measurement with Unobservable Inputs Reconciliations, Recurring Basis, Liability Value	[3]		(258)		(258)		(247)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Noncurrent Payables To Affiliates	[3]				$ 0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	[3]						$ (247)		(207)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings, Description	[3]				0		0
Fair Value Measurement With Unobservable inputs reconciliation Recurring Asset Liability Gain Loss Abstract [Abstract]
Change in collateral	[3]				$ 0		$ 0
Purchases	[3]				0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements	[3]				0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Included in payable for Zion Station decommissioning	[3]						0
Included in regulatory assets/liabilities	[3]				(11)		(40)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales	[3]				0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3	[3]				0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3	[3]				0		0
Fair Value, Inputs, Level 3 [Member] | Commonwealth Edison Co [Member] | Derivative [Member]
Fair Value Measurement With Unobservable inputs reconciliation Recurring Asset Liability Gain Loss Abstract [Abstract]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements	[3]						0
Successor [Member] | Fair Value, Inputs, Level 3 [Member] | Pepco Holdings LLC [Member] | 6311 Life Insurance [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	[4]		2
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Noncurrent Payables To Affiliates	[4]		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	[4]		$ 20		20		0	$ 20
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings, Description	[4]		3
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Issuances			$ (3)	[4]			(3)
Fair Value Measurement With Unobservable inputs reconciliation Recurring Asset Liability Gain Loss Abstract [Abstract]
Change in collateral	[4]		0
Purchases	[4]		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements	[4]		0
The amount of total gains (losses) included in income attributed to the change in unrealized gains (losses) related to assets and liabilities			2
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases, (Sales), Issuances, (Settlements) [Abstract]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Total Gain Loss Included In Earnings Attributed To Changes In Unrealized Gains Losses			2
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Included in regulatory assets/liabilities	[4]		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales	[4]		0
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
Predecessor [Member] | Fair Value, Inputs, Level 3 [Member] | Pepco Holdings LLC [Member] | Preferred Stock [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value		$ 0	18		18		$ 18		3
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings, Description		-18					15
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Issuances		$ 0					$ 0
Fair Value Measurement With Unobservable inputs reconciliation Recurring Asset Liability Gain Loss Abstract [Abstract]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements		0					0
The amount of total gains (losses) included in income attributed to the change in unrealized gains (losses) related to assets and liabilities		0					15
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases, (Sales), Issuances, (Settlements) [Abstract]
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					15
Predecessor [Member] | Fair Value, Inputs, Level 3 [Member] | Pepco Holdings LLC [Member] | 6311 Life Insurance [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value		$ 20	$ 19		$ 19		$ 19		$ 19
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings, Description		1					5
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Issuances		$ 0
Fair Value Measurement With Unobservable inputs reconciliation Recurring Asset Liability Gain Loss Abstract [Abstract]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements		0					$ 2
The amount of total gains (losses) included in income attributed to the change in unrealized gains (losses) related to assets and liabilities		1					3
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases, (Sales), Issuances, (Settlements) [Abstract]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Total Gain Loss Included In Earnings Attributed To Changes In Unrealized Gains Losses		$ 1					$ 3

[1] Includes a reduction for the reclassification of $677 million and $834 million of realized gains due to the settlement of derivative contracts for the years ended December 31, 2016 and 2015, respectively.

[2] Includes $168 million of fair value from contracts acquired as a result of portfolio acquisitions.

[3] Includes $29 million of decreases in fair value and an increase for realized losses due to settlements of $18 million recorded in purchased power expense associated with floating-to-fixed energy swap contracts with unaffiliated suppliers for the year ended December 31, 2016. Includes $55 million of decreases in fair value and a reduction for realized losses due to settlements of $(15) million for the year ended December 31, 2015.

[4] Successor period represents activity from March 24, 2016 to December 31, 2016. See tables below for PHI's predecessor periods, as well as activity for Pepco and DPL for the year ended December 31, 2016.