Changes in Accumulated Other Comprehensive Income - Schedule of Changes in AOCI (Details) - USD ($) $ in Millions		3 Months Ended	12 Months Ended
		Mar. 23, 2016	Dec. 31, 2016	Dec. 31, 2015		Dec. 31, 2014		Dec. 31, 2013
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest			$ 27,612	$ 27,294		$ 24,133		$ 22,940
OCI before reclassifications			186	136	[1]
Amounts reclassified from AOCI	[2]		150	196	[1],[3]
Other comprehensive income (loss)			(36)	60	[1]	(644)
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest			(17)	(19)	[1]	(28)	[1]
OCI before reclassifications			6	12	[1]
Amounts reclassified from AOCI			8	21	[1],[3]
Other comprehensive income (loss)			2	9	[1]
Accumulated Net Unrealized Investment Gain (Loss) [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest			4	3	[1]	3
OCI before reclassifications			(1)
Other comprehensive income (loss)			1
Accumulated Defined Benefit Plans Adjustment [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest			(2,610)	(2,565)	[1]	(2,640)
OCI before reclassifications			182	100	[1]
Amounts reclassified from AOCI			137	175	[1],[2],[3]
Other comprehensive income (loss)			(45)	75	[1]
Accumulated Translation Adjustment [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest			(30)	(40)	[1]	(19)
OCI before reclassifications			(5)	21
Amounts reclassified from AOCI			5
Other comprehensive income (loss)			10	(21)	[1]
Accumulated Equity Investment [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest			(7)	(3)	[1]
OCI before reclassifications			4	3	[1]
Other comprehensive income (loss)			(4)	(3)	[1]
AOCI Including Portion Attributable to Noncontrolling Interest [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest			(2,660)	(2,624)		(2,684)
Exelon Generation Co L L C [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
OCI before reclassifications			4	32	[1]
Amounts reclassified from AOCI	[2]		13	5	[1],[3]
Other comprehensive income (loss)			9	(27)	[1]	(250)
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]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest			(19)	(21)	[1]	(18)	[1]
OCI before reclassifications			6	8	[1]
Amounts reclassified from AOCI			8	5	[1],[3]
Other comprehensive income (loss)			2	(3)	[1]
Exelon Generation Co L L C [Member] | Accumulated Net Unrealized Investment Gain (Loss) [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest			2	1	[1]	1	[1]
OCI before reclassifications			(1)
Other comprehensive income (loss)			1
Exelon Generation Co L L C [Member] | Accumulated Translation Adjustment [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest			(30)	(40)	[1]	(19)
OCI before reclassifications			(5)	21	[1]
Amounts reclassified from AOCI			5
Other comprehensive income (loss)			10	(21)	[1]
Exelon Generation Co L L C [Member] | Accumulated Equity Investment [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest			(7)	(3)	[1]
OCI before reclassifications			4	3	[1]
Other comprehensive income (loss)			(4)	(3)	[1]
Exelon Generation Co L L C [Member] | AOCI Including Portion Attributable to Noncontrolling Interest [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest			(54)	(63)		(36)
PECO Energy Co [Member] | Accumulated Net Unrealized Investment Gain (Loss) [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest			1	1	[1]	1	[1]
PECO Energy Co [Member] | AOCI Including Portion Attributable to Noncontrolling Interest [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest			$ 1	1		1
Predecessor [Member] | Pepco Holdings LLC [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
OCI before reclassifications	[1],[3]			(5)
Amounts reclassified from AOCI	[2]	$ 1		5	[1],[3]
Other comprehensive income (loss)		1		10	[1]	(12)
Predecessor [Member] | Pepco Holdings LLC [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest		(8)		(8)	[1]	(9)	[1]
Amounts reclassified from AOCI	[1]			1
Other comprehensive income (loss)	[1]			1
Predecessor [Member] | Pepco Holdings LLC [Member] | Accumulated Defined Benefit Plans Adjustment [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest		(27)		(28)	[1]	(37)	[1]
OCI before reclassifications	[1]			(5)
Amounts reclassified from AOCI		1		4	[1],[2],[3]
Other comprehensive income (loss)		1		9	[1]
Predecessor [Member] | Pepco Holdings LLC [Member] | AOCI Including Portion Attributable to Noncontrolling Interest [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest		$ (35)		$ (36)		$ (46)

[1] All amounts are net of tax and noncontrolling interests. Amounts in parenthesis represent a decrease in accumulated other comprehensive income.

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

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