Income Taxes - Narrative (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended		12 Months Ended
	Mar. 23, 2016	Dec. 31, 2015	Mar. 31, 2013	Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 15, 2016	Mar. 31, 2016	Mar. 24, 2016	Dec. 15, 2015	Dec. 31, 2013	Dec. 31, 1999
Income Taxes [Line Items]
Tax positions for which there is uncertainty about the timing of tax benefits		$ 415		$ 83		$ 83	$ 415	$ 1,122
Unrecognized Tax Benefits that Would Impact Effective Tax Rate		538		633		633	538	701
Unrecognized Tax Benefits		1,078		916		916	1,078	1,829					$ 2,175
Unrecognized Tax Benefits, Increase Resulting from Settlements with Taxing Authorities						8
Common Stock, Value, Issued		(1,112)		(1,485)		(1,485)	(1,112)				$ 59
Deferred Tax Assets, State Taxes				1		1
Unrecognized Tax Benefits						21	116	1
IRS asserted penalties for understatement of tax						106
Taxes accrued		293		723		723	293
Unrecognized Tax Benefits, Income Tax Penalties Accrued				106		106
Exelon Generation Co L L C [Member]
Income Taxes [Line Items]
Tax positions for which there is uncertainty about the timing of tax benefits		20		7		7	20	680
Unrecognized Tax Benefits that Would Impact Effective Tax Rate		509		483		483	509	672
Unrecognized Tax Benefits		534		490		490	534	1,357					1,415
Unrecognized Tax Benefits, Increase Resulting from Settlements with Taxing Authorities						14
Common Stock, Value, Issued		(425)		(403)		(403)	(425)
Deferred Tax Assets, State Taxes				6		6
Allocation of federal tax benefit under tax sharing agreement		57		94		94	57	55
Unrecognized Tax Benefits						20	112	2
Taxes accrued		186		239		239	186
Unrecognized Tax Benefits, Income Tax Penalties Accrued				0		0
Baltimore Gas and Electric Company [Member]
Income Taxes [Line Items]
Unrecognized Tax Benefits		120		120		120	120	0	$ 120			$ 120	0
Common Stock, Value, Issued		(27)		(27)		(27)	(27)
Proceeds from Contributions from Parent						61	7	0
Allocation of federal tax benefit under tax sharing agreement		7		8		8	7
Unrecognized Tax Benefits						0	0	0
Taxes accrued		23		78		78	23
Unrecognized Tax Benefits, Income Tax Penalties Accrued				0		0
Potomac Electric Power Company [Member]
Income Taxes [Line Items]
Unrecognized Tax Benefits that Would Impact Effective Tax Rate				21		21
Unrecognized Tax Benefits		8		80		80	8	0	59			8	45
Common Stock, Value, Issued		(42)		(66)		(66)	(42)
Tax Adjustments, Settlements, and Unusual Provisions		6
Unrecognized Tax Benefits, Interest on Income Taxes Expense		3
Proceeds from Contributions from Parent						187	112	80
Unrecognized Tax Benefits						0	0	0
Taxes accrued		56		48		48	56
Unrecognized Tax Benefits, Income Tax Penalties Accrued				0		0
Delmarva Power and Light Company [Member]
Income Taxes [Line Items]
Unrecognized Tax Benefits that Would Impact Effective Tax Rate				16		16
Unrecognized Tax Benefits		3		37		37	3	0	21			3	3
Common Stock, Value, Issued		(29)		(34)		(34)	(29)
Tax Adjustments, Settlements, and Unusual Provisions		3
Proceeds from Contributions from Parent						152	75	130
Unrecognized Tax Benefits						0	0	0
Taxes accrued		3		4		4	3
Unrecognized Tax Benefits, Income Tax Penalties Accrued				0		0
Commonwealth Edison Co [Member]
Income Taxes [Line Items]
Tax positions for which there is uncertainty about the timing of tax benefits		142		(12)		(12)	142	149
Unrecognized Tax Benefits		142		(12)		(12)	142	149					324
Common Stock, Value, Issued		(270)		(351)		(351)	(270)
Proceeds from Contributions from Parent						315	202	273
Unrecognized Tax Benefits						0	0	0
IRS asserted penalties for understatement of tax						86
Taxes accrued		63		330		330	63
Unrecognized Tax Benefits, Income Tax Penalties Accrued				86		86
PECO Energy Co [Member]
Income Taxes [Line Items]
Tax positions for which there is uncertainty about the timing of tax benefits								43
Unrecognized Tax Benefits		0		0		0	0	44					44
Common Stock, Value, Issued		(105)		(99)		(99)	(105)
Proceeds from Contributions from Parent						18	16	24
Allocation of federal tax benefit under tax sharing agreement		16		18		18	16	25
Unrecognized Tax Benefits						0	0	0
Taxes accrued		4		4		4	4
Unrecognized Tax Benefits, Income Tax Penalties Accrued				0		0
Pepco Holdings LLC [Member] | Successor [Member]
Income Taxes [Line Items]
Unrecognized Tax Benefits that Would Impact Effective Tax Rate				93		93
Unrecognized Tax Benefits		22		172		172	22		$ 80
Common Stock, Value, Issued				(225)		(225)
Proceeds from Contributions from Parent				1,251
Fresh-Start Adjustment, Increase (Decrease), Deferred Income Tax Liabilities, Noncurrent				35		35
Unrecognized Tax Benefits						0
Taxes accrued				65		65
Pepco Holdings LLC [Member] | Predecessor [Member]
Income Taxes [Line Items]
Tax positions for which there is uncertainty about the timing of tax benefits								686
Unrecognized Tax Benefits that Would Impact Effective Tax Rate		11					11	15
Unrecognized Tax Benefits		22					22	702				$ 11	743
Common Stock, Value, Issued		(103)					(103)				$ 8
Tax Adjustments, Settlements, and Unusual Provisions		35
Federal Income Tax Expense (Benefit), Continuing Operations		26
Discontinued Operation, Tax Effect of Discontinued Operation		9
Unrecognized Tax Benefits, Interest on Income Taxes Expense		21
Unrecognized Tax Benefits							0	0
Taxes accrued		77					77
Atlantic City Electric Company [Member]
Income Taxes [Line Items]
Unrecognized Tax Benefits that Would Impact Effective Tax Rate				22		22
Unrecognized Tax Benefits		0		22		22	0	0					$ 3
Common Stock, Value, Issued		(18)		(34)		(34)	(18)
Tax Adjustments, Settlements, and Unusual Provisions		3
Proceeds from Contributions from Parent						139	95	0
Unrecognized Tax Benefits						0	0	0
Taxes accrued		$ 23		9		9	23
Unrecognized Tax Benefits, Income Tax Penalties Accrued				0		0
Internal Revenue Service (IRS) [Member]
Income Taxes [Line Items]
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit				146		146
Deferred						607	566	576
Internal Revenue Service (IRS) [Member] | Exelon Generation Co L L C [Member]
Income Taxes [Line Items]
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit				19		19
Deferred						(247)	16	(35)
Internal Revenue Service (IRS) [Member] | Baltimore Gas and Electric Company [Member]
Income Taxes [Line Items]
Deferred						88	126	90
Internal Revenue Service (IRS) [Member] | Potomac Electric Power Company [Member]
Income Taxes [Line Items]
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit				21		21
Deferred						136	126	150
Internal Revenue Service (IRS) [Member] | Delmarva Power and Light Company [Member]
Income Taxes [Line Items]
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit				16		16
Deferred						97	73	98
Internal Revenue Service (IRS) [Member] | Commonwealth Edison Co [Member]
Income Taxes [Line Items]
Deferred						379	310	395
Internal Revenue Service (IRS) [Member] | PECO Energy Co [Member]
Income Taxes [Line Items]
Deferred						72	69	87
Internal Revenue Service (IRS) [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Income Taxes [Line Items]
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit				59		59
Deferred				283
Internal Revenue Service (IRS) [Member] | Pepco Holdings LLC [Member] | Predecessor [Member]
Income Taxes [Line Items]
Deferred	$ 10						103	261
Internal Revenue Service (IRS) [Member] | Atlantic City Electric Company [Member]
Income Taxes [Line Items]
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit				22		22
Deferred						22	27	31
State and Local Jurisdiction [Member]
Income Taxes [Line Items]
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit				244		244
Unrecognized Tax Benefits that Would Impact Effective Tax Rate				44		44
Deferred						79	208	(53)
State and Local Jurisdiction [Member] | Exelon Generation Co L L C [Member]
Income Taxes [Line Items]
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit				44		44
Deferred						(1)	49	(137)
State and Local Jurisdiction [Member] | Baltimore Gas and Electric Company [Member]
Income Taxes [Line Items]
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit				120		120
Deferred						31	39	27
State and Local Jurisdiction [Member] | Potomac Electric Power Company [Member]
Income Taxes [Line Items]
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit				59		59
Deferred						16	24	24
State and Local Jurisdiction [Member] | Delmarva Power and Light Company [Member]
Income Taxes [Line Items]
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit				21		21
Deferred						12	1	13
State and Local Jurisdiction [Member] | Commonwealth Edison Co [Member]
Income Taxes [Line Items]
Deferred						63	45	39
State and Local Jurisdiction [Member] | PECO Energy Co [Member]
Income Taxes [Line Items]
Deferred						5	20	1
State and Local Jurisdiction [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Income Taxes [Line Items]
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit				80		80
Deferred				13
State and Local Jurisdiction [Member] | Pepco Holdings LLC [Member] | Predecessor [Member]
Income Taxes [Line Items]
Deferred	$ 7						32	41
State and Local Jurisdiction [Member] | Atlantic City Electric Company [Member]
Income Taxes [Line Items]
Deferred						0	$ 5	$ 7
Like kind exchange [Member]
Income Taxes [Line Items]
Tax Adjustments, Settlements, and Unusual Provisions					$ 106
Income Tax Examination, Interest Expense					94
Deferred						400
Payments for Other Taxes						1,000
Income Taxes Receivable				80		80
Investment Agreement, Early Termination Fee						1,250
Deferred gain on sale of property														$ 1,200
IRS asserted penalties for understatement of tax						90
Expected non-cash charge to earnings			$ 265
Taxes accrued				335		335				$ 360
Unrecognized Tax Benefits, Income Tax Penalties Accrued				1,400		1,400
Like kind exchange [Member] | Commonwealth Edison Co [Member]
Income Taxes [Line Items]
Tax Adjustments, Settlements, and Unusual Provisions					86
Income Tax Examination, Interest Expense					64
Proceeds from Contributions from Parent					$ 150
Payments for Other Taxes						0
Income Taxes Receivable				345		345
Expected non-cash charge to earnings			172
Noncash contributions from parent			$ 172
Unrecognized Tax Benefits, Income Tax Penalties Accrued				$ 300		$ 300