Derivative Financial Instruments - Summary of Interest Rate and Foreign Currency Hedges (Details) - USD ($) $ in Millions		Dec. 31, 2017	Dec. 31, 2016
Derivative [Line Items]
Mark-to-market derivative assets (current assets)		$ 976	$ 917
Mark-to-market derivative assets (noncurrent assets)		337	492
Derivative Liability, Current		232	282
Derivative Liability, Noncurrent		409	392
Total mark-to-market derivative net assets (liabilities)		6	1
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)		976	917
Mark-to-market derivative assets (noncurrent assets)		334	476
Derivative Liability, Current		211	263
Derivative Liability, Noncurrent		174	153
InterestRateAndForeignExchangeContract [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)		3	8
Mark-to-market derivative assets (noncurrent assets)		6	20
Total mark-to-market derivative assets		9	28
Derivative Liability, Current		2	8
Derivative Liability, Noncurrent		2	4
Total mark-to-market derivative liabilities		4	12
Total mark-to-market derivative net assets (liabilities)		5	16
InterestRateAndForeignExchangeContract [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)		3	8
Mark-to-market derivative assets (noncurrent assets)		3	4
Total mark-to-market derivative assets		6	12
Derivative Liability, Current		2	8
Derivative Liability, Noncurrent		2	4
Total mark-to-market derivative liabilities		4	12
Total mark-to-market derivative net assets (liabilities)		2	0
Designated as Hedging Instrument [Member] | InterestRateAndForeignExchangeContract [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)		0	0
Mark-to-market derivative assets (noncurrent assets)		3	0
Total mark-to-market derivative assets		3	0
Derivative Liability, Current		2	7
Derivative Liability, Noncurrent		0	3
Total mark-to-market derivative liabilities		2	10
Total mark-to-market derivative net assets (liabilities)		1	(10)
Not Designated as Hedging Instrument, Economic Hedge [Member] | InterestRateAndForeignExchangeContract [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)		10	17
Mark-to-market derivative assets (noncurrent assets)		0	11
Total mark-to-market derivative assets		10	28
Derivative Liability, Current		7	13
Derivative Liability, Noncurrent		2	8
Total mark-to-market derivative liabilities		9	21
Total mark-to-market derivative net assets (liabilities)		1	7
Not Designated as Hedging Instrument, Trading [Member] | InterestRateAndForeignExchangeContract [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)		0	4	[1]
Mark-to-market derivative assets (noncurrent assets)		0	1	[1]
Total mark-to-market derivative assets		0	5	[1]
Derivative Liability, Current		0	2	[1]
Derivative Liability, Noncurrent		0	2	[1]
Total mark-to-market derivative liabilities		0	4	[1]
Total mark-to-market derivative net assets (liabilities)		0	1	[1]
Collateral and Netting | InterestRateAndForeignExchangeContract [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)	[2]	(7)	(13)
Mark-to-market derivative assets (noncurrent assets)	[2]	0	(8)
Total mark-to-market derivative assets	[2]	(7)	(21)
Derivative Liability, Current	[2]	(7)	(14)
Derivative Liability, Noncurrent	[2]	0	(9)
Total mark-to-market derivative liabilities	[2]	(7)	(23)
Total mark-to-market derivative net assets (liabilities)	[2]	0	2
Corporate, Non-Segment [Member] | Designated as Hedging Instrument [Member] | InterestRateAndForeignExchangeContract [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)		0	0
Mark-to-market derivative assets (noncurrent assets)		3	16
Total mark-to-market derivative assets		3	16
Derivative Liability, Current		0	0
Derivative Liability, Noncurrent		0	0
Total mark-to-market derivative liabilities		0	0
Total mark-to-market derivative net assets (liabilities)		$ 3	$ 16

[1] Generation enters into interest rate derivative contracts to economically hedge risk associated with the interest rate component of commodity positions. The characterization of the interest rate derivative contracts between the proprietary trading activity in the above table is driven by the corresponding characterization of the underlying commodity position that gives rise to the interest rate exposure. Generation does not utilize proprietary trading interest rate derivatives with the objective of benefiting from shifts or changes in market interest rates.

[2] Exelon and Generation net all available amounts allowed under the derivative authoritative guidance on the balance sheet. These amounts include unrealized derivative transactions with the same counterparty under legally enforceable master netting agreements and cash collateral. In some cases, Exelon and Generation may have other offsetting counterparty exposures subject to a master netting or similar agreement, such as accrued interest, transactions that do not qualify as derivatives, letters of credit and other forms of non-cash collateral, which are not reflected in the table above.