Income Taxes - Schedule of Carryforwards and Corresponding Valuation Allowances (Details) $ in Millions	Dec. 31, 2017 USD ($)
Internal Revenue Service (IRS) [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses	$ 624	[1]
Deferred Tax Assets, Operating Loss Carryforwards	131
Internal Revenue Service (IRS) [Member] | Exelon Generation Co L L C [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses	0
Deferred Tax Assets, Operating Loss Carryforwards	0
Internal Revenue Service (IRS) [Member] | Commonwealth Edison Co [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses	156
Deferred Tax Assets, Operating Loss Carryforwards	33
Internal Revenue Service (IRS) [Member] | PECO Energy Co [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses	7
Deferred Tax Assets, Operating Loss Carryforwards	1
Internal Revenue Service (IRS) [Member] | Baltimore Gas and Electric Company [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses	0
Deferred Tax Assets, Operating Loss Carryforwards	0
Internal Revenue Service (IRS) [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses	261
Deferred Tax Assets, Operating Loss Carryforwards	55
Internal Revenue Service (IRS) [Member] | Potomac Electric Power Company [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses	82
Deferred Tax Assets, Operating Loss Carryforwards	17
Internal Revenue Service (IRS) [Member] | Delmarva Power and Light Company [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses	81
Deferred Tax Assets, Operating Loss Carryforwards	17
Internal Revenue Service (IRS) [Member] | Atlantic City Electric Company [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses	63
Deferred Tax Assets, Operating Loss Carryforwards	13
Internal Revenue Service (IRS) [Member] | General Business Tax Credit Carryforward [Member]
Operating Loss Carryforwards [Line Items]
Federal general business credits carryforwards	861	[2]
Internal Revenue Service (IRS) [Member] | General Business Tax Credit Carryforward [Member] | Exelon Generation Co L L C [Member]
Operating Loss Carryforwards [Line Items]
Federal general business credits carryforwards	868
Internal Revenue Service (IRS) [Member] | General Business Tax Credit Carryforward [Member] | Commonwealth Edison Co [Member]
Operating Loss Carryforwards [Line Items]
Federal general business credits carryforwards	1
Internal Revenue Service (IRS) [Member] | General Business Tax Credit Carryforward [Member] | PECO Energy Co [Member]
Operating Loss Carryforwards [Line Items]
Federal general business credits carryforwards	0
Internal Revenue Service (IRS) [Member] | General Business Tax Credit Carryforward [Member] | Baltimore Gas and Electric Company [Member]
Operating Loss Carryforwards [Line Items]
Federal general business credits carryforwards	1
Internal Revenue Service (IRS) [Member] | General Business Tax Credit Carryforward [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Operating Loss Carryforwards [Line Items]
Federal general business credits carryforwards	5
Internal Revenue Service (IRS) [Member] | General Business Tax Credit Carryforward [Member] | Potomac Electric Power Company [Member]
Operating Loss Carryforwards [Line Items]
Federal general business credits carryforwards	0
Internal Revenue Service (IRS) [Member] | General Business Tax Credit Carryforward [Member] | Delmarva Power and Light Company [Member]
Operating Loss Carryforwards [Line Items]
Federal general business credits carryforwards	0
Internal Revenue Service (IRS) [Member] | General Business Tax Credit Carryforward [Member] | Atlantic City Electric Company [Member]
Operating Loss Carryforwards [Line Items]
Federal general business credits carryforwards	0
State and Local Jurisdiction [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses	3,555	[3]
Deferred taxes on state tax attributes (net)	233
Valuation allowance on state tax attributes	29
State and Local Jurisdiction [Member] | Exelon Generation Co L L C [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses	1,479	[3]
Deferred taxes on state tax attributes (net)	97
Valuation allowance on state tax attributes	23
State and Local Jurisdiction [Member] | Commonwealth Edison Co [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses	0
Deferred taxes on state tax attributes (net)	0
Valuation allowance on state tax attributes	0
State and Local Jurisdiction [Member] | PECO Energy Co [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses	98	[4]
Deferred taxes on state tax attributes (net)	8
Valuation allowance on state tax attributes	0
State and Local Jurisdiction [Member] | Baltimore Gas and Electric Company [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses	177	[5]
Deferred taxes on state tax attributes (net)	12
Valuation allowance on state tax attributes	1
State and Local Jurisdiction [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses	1,440	[6]
Deferred taxes on state tax attributes (net)	98
Valuation allowance on state tax attributes	5
State and Local Jurisdiction [Member] | Potomac Electric Power Company [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses	347	[7]
Deferred taxes on state tax attributes (net)	23
Valuation allowance on state tax attributes	0
State and Local Jurisdiction [Member] | Delmarva Power and Light Company [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses	753	[8]
Deferred taxes on state tax attributes (net)	51
Valuation allowance on state tax attributes	0
State and Local Jurisdiction [Member] | Atlantic City Electric Company [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses	299	[9]
Deferred taxes on state tax attributes (net)	21
Valuation allowance on state tax attributes	$ 0

[1] Exelon's federal net operating loss will begin expiring in 2034.

[2] Exelon’s federal general business credit carryforwards will begin expiring in 2033.

[3] Exelon’s and Generation's state net operating losses and credit carryforwards, which are presented on a post-apportioned basis, will begin expiring in 2018.

[4] PECO's state net operating loss carryforwards, which are presented on a post-apportioned basis, will begin expiring in 2031.

[5] BGE's state net operating loss carryforwards, which are presented on a post-apportioned basis, will begin expiring in 2026.

[6] PHI's state net operating loss carryforwards, which are presented on a post-apportioned basis, will begin expiring in 2036.

[7] Pepco's state net operating loss carryforwards, which are presented on a post-apportioned basis, will begin expiring in 2028.

[8] DPL's state net operating loss carryforwards, which are presented on a post-apportioned basis, will begin expiring in 2027.

[9] ACE's state net operating loss carryforwards, which are presented on a post-apportioned basis, will begin expiring in 2031.