Changes in Accumulated Other Comprehensive Income - Schedule of Changes in AOCI (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2017		Mar. 31, 2016		Mar. 23, 2016	Dec. 31, 2016		Dec. 31, 2015
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Net current-period OCI		$ (12)		$ 28
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest		28,291					$ 27,612
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
OCI before reclassifications	[1]	2		(10)
Amounts reclassified from AOCI	[1],[2]	4		3
Net current-period OCI	[1]	6		(7)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	[1]	(11)		(26)					$ (19)
Accumulated Net Unrealized Investment Gain (Loss) [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
OCI before reclassifications	[1]	1		(1)
Amounts reclassified from AOCI		0		0
Net current-period OCI	[1]	1		(1)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest		5	[1]	2	[1]		4	[1]	3
Accumulated Defined Benefit Plans Adjustment [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
OCI before reclassifications		(59)	[1]	(1)
Amounts reclassified from AOCI	[1],[2],[3]	36		34
Net current-period OCI	[1]	(23)		33
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	[1]	(2,633)		(2,532)			(2,610)		(2,565)
Accumulated Translation Adjustment [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
OCI before reclassifications	[1]	1		6
Amounts reclassified from AOCI		0		0
Net current-period OCI	[1]	1		6
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest		(29)	[1]	(34)	[1]		(30)	[1]	(40)
Accumulated Equity Investment [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
OCI before reclassifications	[1]	5		(3)
Amounts reclassified from AOCI	[1],[2]	0		0
Net current-period OCI	[1]	5		(3)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	[1]	(2)		(6)			(7)		(3)
AOCI Attributable to Parent [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
OCI before reclassifications	[1]	(50)		(9)
Amounts reclassified from AOCI	[1]	(40)		37	[2]
Net current-period OCI	[1]	(10)		28
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	[1]	(2,670)		(2,596)			(2,660)		(2,624)
Exelon Generation Co L L C [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Net current-period OCI		11		(1)
Exelon Generation Co L L C [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
OCI before reclassifications	[1]	2		(8)
Amounts reclassified from AOCI	[1],[2]	4		3
Net current-period OCI	[1]	6		(5)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest		(13)	[1]	(26)	[1]				(21)
Exelon Generation Co L L C [Member] | Accumulated Net Unrealized Investment Gain (Loss) [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
OCI before reclassifications	[1]	0		0
Amounts reclassified from AOCI		0		0
Net current-period OCI	[1]	0		0
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest		2	[1]	1	[1]		2		1	[1]
Exelon Generation Co L L C [Member] | Accumulated Defined Benefit Plans Adjustment [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
OCI before reclassifications		0		0
Amounts reclassified from AOCI		0		0
Net current-period OCI		0		0
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest		0		0	[1]		0		0	[1]
Exelon Generation Co L L C [Member] | Accumulated Translation Adjustment [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
OCI before reclassifications	[1]	1		6
Amounts reclassified from AOCI		0		0
Net current-period OCI	[1]	1		6
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest		(29)	[1]	(34)	[1]		(30)	[1]	(40)
Exelon Generation Co L L C [Member] | Accumulated Equity Investment [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
OCI before reclassifications	[1]	6		(2)
Amounts reclassified from AOCI	[1],[2]	0		0
Net current-period OCI	[1]	6		(2)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	[1]	(1)		(5)			(7)		(3)
Exelon Generation Co L L C [Member] | AOCI Attributable to Parent [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
OCI before reclassifications	[1]	9		(4)
Amounts reclassified from AOCI	[1]	(4)		3	[2]
Net current-period OCI	[1]	13		(1)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	[1]	(41)		(64)			(54)		(63)
PECO Energy Co [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
OCI before reclassifications		0		0	[1]
Amounts reclassified from AOCI		0		0
Net current-period OCI		0		0
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	[1]	0		0			0		0
PECO Energy Co [Member] | Accumulated Net Unrealized Investment Gain (Loss) [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
OCI before reclassifications		0		0	[1]
Amounts reclassified from AOCI		0		0
Net current-period OCI		0		0
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest		1	[1]	1	[1]		1	[1]	1
PECO Energy Co [Member] | Accumulated Defined Benefit Plans Adjustment [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
OCI before reclassifications		0		0
Amounts reclassified from AOCI		0		0
Net current-period OCI		0		0
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest		0		0			0		0
PECO Energy Co [Member] | Accumulated Translation Adjustment [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
OCI before reclassifications		0		0	[1]
Amounts reclassified from AOCI		0		0
Net current-period OCI		0		0
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest		0		0			0		0
PECO Energy Co [Member] | Accumulated Equity Investment [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
OCI before reclassifications		0		0	[1]
Amounts reclassified from AOCI		0		0
Net current-period OCI		0		0
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest		0		0			0		0
PECO Energy Co [Member] | AOCI Attributable to Parent [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
OCI before reclassifications	[1]	0		0
Amounts reclassified from AOCI		0	[1]	0
Net current-period OCI		0	[1]	0
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	[1]	$ 1		1			$ 1		1
PEPCO Holdings Inc [Member] | Accumulated Defined Benefit Plans Adjustment [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Amounts reclassified from AOCI				$ 1
PEPCO Holdings Inc [Member] | Predecessor [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
OCI before reclassifications						$ 0
Amounts reclassified from AOCI						0
Net current-period OCI						0
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest						(8)			(8)
PEPCO Holdings Inc [Member] | Predecessor [Member] | Accumulated Net Unrealized Investment Gain (Loss) [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
OCI before reclassifications						0
Amounts reclassified from AOCI						0
Net current-period OCI						0
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest						0			0
PEPCO Holdings Inc [Member] | Predecessor [Member] | Accumulated Defined Benefit Plans Adjustment [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
OCI before reclassifications						0
Amounts reclassified from AOCI						1
Net current-period OCI						1
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest						(27)			(28)
PEPCO Holdings Inc [Member] | Predecessor [Member] | Accumulated Translation Adjustment [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
OCI before reclassifications						0
Amounts reclassified from AOCI						0
Net current-period OCI						0
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest						0			0
PEPCO Holdings Inc [Member] | Predecessor [Member] | Accumulated Equity Investment [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
OCI before reclassifications						0
Amounts reclassified from AOCI						0
Net current-period OCI						0
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest						0			0
PEPCO Holdings Inc [Member] | Predecessor [Member] | AOCI Attributable to Parent [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
OCI before reclassifications						0
Amounts reclassified from AOCI						1
Net current-period OCI						1
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest						$ (35)			$ (36)

[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.