Fair Value of Financial Assets and Liabilities (Fair Value Assets Liabilities Measured On Recurring Basis Unobservable Input Reconciliation) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended						12 Months Ended			12 Months Ended																				12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2013 Fair Value Inputs Level 3 [Member]	Dec. 31, 2012 Fair Value Inputs Level 3 [Member]	Dec. 31, 2013 Nuclear Decommissioning Trust Fund Investment Level Three Asset [Member]	Dec. 31, 2011 Nuclear Decommissioning Trust Fund Investment Level Three Asset [Member]	Dec. 31, 2012 Nuclear Decommissioning Trust Fund Investment Level Three Asset [Member] Fair Value Inputs Level 3 [Member]	Dec. 31, 2013 Pledged Assets For Zion Station Decommissioning [Member]	Dec. 31, 2011 Pledged Assets For Zion Station Decommissioning [Member]	Dec. 31, 2012 Pledged Assets For Zion Station Decommissioning [Member] Fair Value Inputs Level 3 [Member]	Dec. 31, 2013 Derivative [Member]		Dec. 31, 2012 Derivative [Member]		Dec. 31, 2013 Derivative [Member] Fair Value Inputs Level 3 [Member]		Dec. 31, 2012 Derivative [Member] Fair Value Inputs Level 3 [Member]		Dec. 31, 2013 Other Investments [Member]	Dec. 31, 2012 Other Investments [Member]	Dec. 31, 2013 Exelon Generation Co L L C [Member]	Dec. 31, 2012 Exelon Generation Co L L C [Member]	Dec. 31, 2013 Exelon Generation Co L L C [Member] Fair Value Inputs Level 3 [Member]	Dec. 31, 2012 Exelon Generation Co L L C [Member] Fair Value Inputs Level 3 [Member]	Dec. 31, 2013 Exelon Generation Co L L C [Member] Nuclear Decommissioning Trust Fund Investment Level Three Asset [Member]	Dec. 31, 2012 Exelon Generation Co L L C [Member] Nuclear Decommissioning Trust Fund Investment Level Three Asset [Member]	Dec. 31, 2013 Exelon Generation Co L L C [Member] Nuclear Decommissioning Trust Fund Investment Level Three Asset [Member] Fair Value Inputs Level 3 [Member]	Dec. 31, 2012 Exelon Generation Co L L C [Member] Nuclear Decommissioning Trust Fund Investment Level Three Asset [Member] Fair Value Inputs Level 3 [Member]	Dec. 31, 2011 Exelon Generation Co L L C [Member] Pledged Assets For Zion Station Decommissioning [Member]	Dec. 31, 2013 Exelon Generation Co L L C [Member] Pledged Assets For Zion Station Decommissioning [Member] Fair Value Inputs Level 3 [Member]	Dec. 31, 2012 Exelon Generation Co L L C [Member] Pledged Assets For Zion Station Decommissioning [Member] Fair Value Inputs Level 3 [Member]	Dec. 31, 2013 Exelon Generation Co L L C [Member] Derivative [Member]	Dec. 31, 2012 Exelon Generation Co L L C [Member] Derivative [Member]	Dec. 31, 2013 Exelon Generation Co L L C [Member] Derivative [Member] Fair Value Inputs Level 3 [Member]		Dec. 31, 2012 Exelon Generation Co L L C [Member] Derivative [Member] Fair Value Inputs Level 3 [Member]		Dec. 31, 2013 Exelon Generation Co L L C [Member] Other Investments [Member]	Dec. 31, 2012 Exelon Generation Co L L C [Member] Other Investments [Member]	Dec. 31, 2013 Exelon Generation Co L L C [Member] Other Investments [Member] Fair Value Inputs Level 3 [Member]	Dec. 31, 2013 Commonwealth Edison Co [Member] Derivative [Member] Fair Value Inputs Level 3 [Member]		Dec. 31, 2012 Commonwealth Edison Co [Member] Derivative [Member] Fair Value Inputs Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Beginning balance	$ 656		$ 656	$ 67	$ 183	$ 13		$ 89	$ 37		$ 367				$ 367	[1]	$ 17	[1]	$ 17				$ 949	$ 867		$ (13)	$ 183		$ (37)	$ 89				$ 660		$ 817		$ 17			$ (293)		$ (800)
Total realized / unrealized gains (losses)
Included in income	(42)			59	2		0	0			(44)	[2]					59	[1],[3]					(49)	(66)	2			0						(51)	[2]	(66)	[4]
Included in other comprehensive income	2			0	0			0									0	[1]	2				217	475										219		475	[5]	2
Included in payable for Zion Station decommissioning																								0				0
Included in regulatory assets	(118)			40	8		1	0			(126)	[6]					39	[1]																							100	[7],[8]	507	[10],[9]
Included in noncurrent payables to affiliates																						1	(8)			1	(8)
Change in collateral	7	(32)			0			0			7						(32)	[1]					(7)	32										(7)		32
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Purchases Sales Issuances Settlements [Abstract]
Purchases	297			583	203		169	62		63	28						334	[1],[11]	4	17			297	583			203	169		62	63			28		334	[11]		17	4
Sales	(86)			(11)	(28)			(39)		(11)	(11)								(8)				86	11	(28)					39	11	(11)						(8)
Settlements	(18)				(18)																18				18
Transfers into Level 3 - (Asset) / Liability		(39)	87										(39)	[1]	86				1			(39)	(87)										(39)	(86)				1
Transfers out of Level 3 - (Asset) / Liability	(36)			(89)	0			0			(35)						(89)	[1]	(1)				(36)	(89)										(35)		(89)		(1)
Ending balance	749	656		656	350	13	183	112	37	89	272		367				367	[1]	15	17			942	949			350	183	(37)	112	89			465		660			17	15	(193)		(293)
The amount of total gains (losses) included in income attributed to the change in unrealized gains (losses) related to assets and liabilities	168			214	1		0	0			167						214	[1]					157	(165)	1			0						156		(165)
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Gain (loss) reclassified to results of operating due to the settlement of derivative contracts	(211)
Fair value of Constellation fair value assets acquired															310
Acquisition of marketable securities															$ 14

[1] Excludes $98 million of increases in fair value and $566 million of realized losses due to settlements for the year ended December 31, 2012 of Generation’s financial swap contract with ComEd, which eliminates upon consolidation in Exelon’s Consolidated Financial Statements. This position was de-designated as a cash flow hedge prior to the merger date.

[2] Includes a reduction for the reclassification of $211 million of realized gains due to settlement of derivative contracts recorded in results of operations for the year ended December 31, 2013.

[3] Includes a reduction for the reclassification of $155 million of realized gains due to the settlement of derivative contracts recorded in results of operations for the year ended December 31, 2012.

[4] Includes a reduction for the reclassification of $99 million of realized gains due to the settlement of derivative contracts recorded in results of operations for the year ended December 31, 2012.

[5] Includes $98 million of increases in fair value and $566 million of realized losses reclassified from OCI due to settlements associated with Generation's financial swap contract with ComEd for the year ended December 31, 2012. This position was de-designated as a cash flow hedge prior to the merger date. All prospective changes in fair value and reclassifications of realized amounts are being recorded to income offset by the amortization of the frozen mark in OCI. All items eliminate upon consolidation in Exelon's Consolidated Financial Statements.

[6] Excludes decreases in fair value of $11 million of and realized losses reclassified due to settlements of $215 million associated with Generation’s financial swap contract with ComEd for the year ended December 31, 2013

[7] Includes $11 million of increases in fair value and realized losses due to settlements of $215 million associated with Generation's financial swap contract with ComEd for the year ended December 31, 2013. All items eliminate upon consolidation in Exelon's Consolidated Financial Statements.

[8] Includes $126 million of increases in the fair value and realized losses due to settlements of $7 million recorded in purchased power expense associated with floating-to-fixed energy swap contracts with unaffiliated suppliers for the year ended December 31, 2013

[9] Includes $98 million of increases in fair value and $566 million of realized gains due to settlements associated with ComEd's financial swap contract with Generation for the year ended December 31, 2012. All items eliminate upon consolidation in Exelon's Consolidated Financial Statements.

[10] Includes $34 million of decreases in the fair value and realized losses due to settlements of $5 million recorded in purchased power expense associated with floating-to-fixed energy swap contracts with unaffiliated suppliers for the year ended December 31, 2012

[11] Includes $310 million of fair value from contracts and $14 million of other investments acquired as a result of the merger.