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	3 Months Ended
	Mar. 31, 2014		Mar. 31, 2013
Fair Value Inputs Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Beginning balance	$ 749		$ 656
Total realized / unrealized gains (losses)
Included in income	311		126
Included in other comprehensive income			0
Included in payable for Zion Station decommissioning	(1)
Included in regulatory assets	(28)		7
Change in collateral	144		33
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Purchases Sales Issuances Settlements [Abstract]
Purchases	181		49
Sales	(7)		26
Settlements	(6)
Transfers into Level 3 - (Asset) / Liability	(26)
Transfers out of Level 3 - (Asset) / Liability	1		4
Ending balance	752		583
The amount of total gains (losses) included in income attributed to the change in unrealized gains (losses) related to assets and liabilities	(446)		(78)
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Fair value of Constellation fair value assets acquired			10
Nuclear Decommissioning Trust Fund Investment Level Three Asset [Member] | Fair Value Inputs Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Beginning balance	350		183
Total realized / unrealized gains (losses)
Included in income	(1)		(1)
Included in regulatory assets	(3)		(1)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Purchases Sales Issuances Settlements [Abstract]
Purchases	139		32
Sales	(1)		7
Settlements	(6)
Ending balance	486		210
The amount of total gains (losses) included in income attributed to the change in unrealized gains (losses) related to assets and liabilities	0		1
Pledged Assets For Zion Station Decommissioning [Member] | Fair Value Inputs Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Beginning balance	112		89
Total realized / unrealized gains (losses)
Included in payable for Zion Station decommissioning	(1)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Purchases Sales Issuances Settlements [Abstract]
Purchases	30		22
Sales	(4)		7
Ending balance	137		104
Derivative [Member] | Fair Value Inputs Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Beginning balance	272		367
Total realized / unrealized gains (losses)
Included in income	312	[1],[2]	127	[3]
Included in other comprehensive income			0	[4]
Included in regulatory assets	(25)	[5]	8	[6]
Change in collateral	144		33
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Purchases Sales Issuances Settlements [Abstract]
Purchases	10		(5)	[7]
Sales	(2)		4
Transfers into Level 3 - (Asset) / Liability	(26)
Transfers out of Level 3 - (Asset) / Liability	8		4
Ending balance	119		260
The amount of total gains (losses) included in income attributed to the change in unrealized gains (losses) related to assets and liabilities	(446)		(79)
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	(58)		58
Increase (decrease) in fair value related to the swap contract			8
Realized gains (losses) related to swap contract			133
Other Investments [Member] | Fair Value Inputs Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Beginning balance	15		17
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Purchases Sales Issuances Settlements [Abstract]
Purchases	2		0
Sales	0		8
Transfers out of Level 3 - (Asset) / Liability	(7)
Ending balance	10		9
Exelon Generation Co L L C [Member]
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	(134)
Increase (decrease) in fair value related to the swap contract	0
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Beginning balance	942		949
Total realized / unrealized gains (losses)
Included in income	311		143
Included in other comprehensive income	0		124
Included in payable for Zion Station decommissioning	(1)
Included in regulatory assets	(3)
Included in noncurrent payables to affiliates			1
Change in collateral	144		33
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Purchases Sales Issuances Settlements [Abstract]
Purchases	181	[8]	49
Sales	(7)		(26)
Settlements	(6)
Transfers into Level 3 - (Asset) / Liability	(26)
Transfers out of Level 3 - (Asset) / Liability	1		4
Ending balance	920		743
The amount of total gains (losses) included in income attributed to the change in unrealized gains (losses) related to assets and liabilities	(446)		(85)
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Fair value of Constellation fair value assets acquired			323
Acquisition of marketable securities			17
Exelon Generation Co L L C [Member] | Nuclear Decommissioning Trust Fund Investment Level Three Asset [Member] | Fair Value Inputs Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Beginning balance	350		183
Total realized / unrealized gains (losses)
Included in income	(1)		(1)
Included in regulatory assets	(3)
Included in noncurrent payables to affiliates			1
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Purchases Sales Issuances Settlements [Abstract]
Purchases	139	[8]	32
Sales	(1)		(7)
Settlements	(6)
Ending balance	486		210
The amount of total gains (losses) included in income attributed to the change in unrealized gains (losses) related to assets and liabilities	0		1
Exelon Generation Co L L C [Member] | Pledged Assets For Zion Station Decommissioning [Member] | Fair Value Inputs Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Beginning balance	112		89
Total realized / unrealized gains (losses)
Included in payable for Zion Station decommissioning	(1)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Purchases Sales Issuances Settlements [Abstract]
Purchases	30	[8]	22
Sales	(4)		(7)
Ending balance	137		104
Exelon Generation Co L L C [Member] | Derivative [Member] | Fair Value Inputs Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Beginning balance	465		660
Total realized / unrealized gains (losses)
Included in income	312	[9]	144	[10],[11],[3]
Included in other comprehensive income	0	[8]	124	[12],[6]
Included in regulatory assets	0
Change in collateral	144		33
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Purchases Sales Issuances Settlements [Abstract]
Purchases	10		(5)	[7]
Sales	(2)		(4)
Transfers into Level 3 - (Asset) / Liability	(26)
Transfers out of Level 3 - (Asset) / Liability	8		4
Ending balance	287		420
The amount of total gains (losses) included in income attributed to the change in unrealized gains (losses) related to assets and liabilities	(446)		(86)
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			(58)
Increase (decrease) in fair value related to the swap contract			8
Realized gains (losses) related to swap contract			(147)
Exelon Generation Co L L C [Member] | Other Investments [Member] | Fair Value Inputs Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Beginning balance	15		17
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Purchases Sales Issuances Settlements [Abstract]
Purchases	2		0
Sales	0		(8)
Transfers into Level 3 - (Asset) / Liability	(10)
Transfers out of Level 3 - (Asset) / Liability	(7)
Ending balance			9
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	(193)		(293)
Total realized / unrealized gains (losses)
Included in regulatory assets	(25)	[13],[14]	(133)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Purchases Sales Issuances Settlements [Abstract]
Ending balance	(168)		(160)
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Increase (decrease) in fair value related to the swap contract	0		(135)
Realized gains (losses) related to swap contract	0		133
Realized gains (losses) related to swap contract with unaffiliated parties	(5)
Increase (decrease) in fair value related to floating-to-fixed energy swap contracts	$ (30)		$ 11

[1] ) Includes an increase for the reclassification of $134 million of realized losses due to the settlement of derivative contracts recorded in results of operations for the three months ended March 31, 2014.

[2] Includes the reclassification of $##D<grclrelloss> million and $##D<gpyrclrellossq2q3> million of realized losses due to the settlement of derivative contracts recorded in results of operations for the ##D<threemonth> and ##D<curmonth> months ended ##D<cyperiod>.

[3] Includes the reclassification of $##D<eqtdreclasssettlementpy> million and $##D<eytdreclasssettlementpy> million of realized losses due to the settlement of derivative contracts recorded in results of operations for the ##D<threemonth> and ##D<curmonth> months ended ##D<pyperiod>, respectively.

[4] b)        Excludes increases in fair value of $8 million and realized losses reclassified due to settlements of $133 million associated with Generation’s financial swap contract with ComEd for the three months ended March 31, 2013.

[5] Excludes decreases in fair value of $##D<gcomedfvpretaxqtdq2q3> million and $##D<gcomedfvpretaxytd> million and realized losses reclassified due to settlements of $##D<gcomedreclassqtdq2q3> million and $##D<gcomedreclassytd> million associated with Generation?s financial swap contract with ComEd for the ##D<threemonth> and ##D<curmonth> months ended ##D<cyperiod>. All items eliminate upon consolidation in Exelon's Consolidated Financial Statements.

[6] Excludes $##D<gcomedfvpretaxqtdq2q3py> million and $##D<gcomedfvpretaxytdpy> million of decreases in fair value and $##D<gcomedreclassqtdq2q3py> million and $##D<gcomedreclassytdpy> million of realized losses due to settlements for the ##D<threemonth> and ##D<curmonth> months ended ##D<pyperiod> of Generation?s financial swap contract with ComEd, which eliminates upon consolidation in Exelon?s Consolidated Financial Statements.

[7] Includes $##D<gpyfvacquiredq2q3> million of fair value from contracts and $##D<gpyfvothinvestq2q3> million of other investments acquired as a result of the merger.

[8]

[9] (a)        Includes an increase for the reclassification of $134 million of realized losses due to the settlement of derivative contracts recorded in results of operations.

[10] (a)        Includes the reclassification of $58 million of realized losses due to the settlement of derivative contracts recorded in results of operations.

[11] ) Includes the reclassification of $##D<gqtdreclasssettlementpy> million and $##D<gytdreclasssettlementpy> million of realized losses due to the settlement of derivative contracts recorded in results of operations for the ##D<threemonth> and ##D<curmonth> months ended ##D<pyperiod>, respectively.

[12] (b)        Includes $8 million of increases in fair value and $133 million of realized losses due to settlements during 2013 of Generation's financial swap contract with ComEd, which eliminates upon consolidation in Exelon's Consolidated Financial Statements.

[13] (a)        

[14] Includes $30 million of decrease in the fair value partially offset by realized gains due to settlements of $5 million recorded in purchased power expense associated with floating-to-fixed energy swap contracts with unaffiliated suppliers for the three months ended March 31, 2014.