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Income Taxes - Reconciliation to Effective Tax Rate (Details)
 3 Months Ended 6 Months Ended 9 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Mar. 23, 2016
Sep. 30, 2016
 [3]
Sep. 30, 2017
Sep. 30, 2016
Effective Income Tax Rate Reconciliation, Percent [Abstract]            
U.S. Federal statutory rate 35.00% 35.00%     35.00% 35.00%
Increase (decrease) due to:            
State income taxes, net of Federal income tax benefit 2.20% 3.80%     0.70% 2.50% [1]
Qualified nuclear decommissioning trust fund income 2.60% 4.00%     4.00% 4.80%
Amortization of investment tax credit, including deferred taxes on basis difference (1.10%) (0.90%)     (0.90%) (1.30%)
Plant basis differences (2.60%) (3.00%)     (3.40%) (4.50%)
Production tax credits and other credits (2.20%) (2.90%)     (1.80%) (4.10%)
Noncontrolling interests 0.50% 0.20%     0.20% 0.50%
Statute of limitations expiration   (0.10%)       (0.50%)
EffectiveIncomeTaxRateReconciliationPenalties   4.30%       2.30%
Effective Income Tax Rate Reconciliation, Tax Settlement, Other, Percent   (0.60%)     (5.40%) 6.20%
Fitzpatrick bargain purchase gain (0.20%)       (3.20%)  
Like-kind exchange(a) [2]         (1.70%)  
Other (0.10%) (0.80%)     (0.00%) (1.80%)
Effective income tax rate 34.10% 39.00%     23.50% 39.10%
Exelon Generation Co L L C [Member]            
Effective Income Tax Rate Reconciliation, Percent [Abstract]            
U.S. Federal statutory rate 35.00% 35.00%     35.00% 35.00%
Increase (decrease) due to:            
State income taxes, net of Federal income tax benefit 5.60% 2.60%     2.10% 2.60% [1]
Qualified nuclear decommissioning trust fund income 5.80% 7.80%     14.00% 8.80%
Amortization of investment tax credit, including deferred taxes on basis difference (2.20%) (1.60%)     (2.70%) (2.00%)
Plant basis differences 0.00% 0.00%     0.00% 0.00%
Production tax credits and other credits (4.80%) (5.70%)     (6.20%) (7.60%)
Noncontrolling interests 1.00% 0.50%     0.70% 0.90%
Statute of limitations expiration   0.30%       (1.70%)
EffectiveIncomeTaxRateReconciliationPenalties   0.00%       0.00%
Effective Income Tax Rate Reconciliation, Tax Settlement, Other, Percent   0.00%     (2.50%) 0.00%
Fitzpatrick bargain purchase gain (0.40%)       (11.20%)  
Like-kind exchange(a) [2]         0.00%  
Other 0.30% (0.50%)     (0.40%) (2.10%)
Effective income tax rate 40.30% 38.40%     28.80% 33.90%
Commonwealth Edison Co [Member]            
Effective Income Tax Rate Reconciliation, Percent [Abstract]            
U.S. Federal statutory rate 35.00% 35.00%     35.00% 35.00%
Increase (decrease) due to:            
State income taxes, net of Federal income tax benefit 6.60% 7.30%     5.90% 5.40% [1]
Qualified nuclear decommissioning trust fund income (0.00%) (0.00%)     (0.00%) (0.00%)
Amortization of investment tax credit, including deferred taxes on basis difference (0.20%) (0.60%)     (0.20%) (0.30%)
Plant basis differences (0.30%) (1.90%)     (0.30%) (0.60%)
Production tax credits and other credits 0.00% (0.10%)     0.00% 0.00%
Noncontrolling interests 0.00% 0.00%     0.00% 0.00%
Statute of limitations expiration   0.00%       0.00%
EffectiveIncomeTaxRateReconciliationPenalties   27.20%       5.60%
Effective Income Tax Rate Reconciliation, Tax Settlement, Other, Percent   0.00%     0.00% 0.00%
Fitzpatrick bargain purchase gain 0.00%       0.00%  
Like-kind exchange(a) [2]         1.70%  
Other (0.20%) 0.10%     0.20% (0.00%)
Effective income tax rate 40.90% 67.00%     42.30% 45.10%
PECO Energy Co [Member]            
Effective Income Tax Rate Reconciliation, Percent [Abstract]            
U.S. Federal statutory rate 35.00% 35.00%     35.00% 35.00%
Increase (decrease) due to:            
State income taxes, net of Federal income tax benefit (0.10%) 2.40%     (0.10%) 1.30% [1]
Qualified nuclear decommissioning trust fund income (0.00%) (0.00%)     (0.00%) (0.00%)
Amortization of investment tax credit, including deferred taxes on basis difference (0.10%) (0.10%)     (0.10%) (0.10%)
Plant basis differences (14.60%) (6.70%)     (14.40%) (8.80%)
Production tax credits and other credits 0.00% 0.00%     0.00% 0.00%
Noncontrolling interests 0.00% 0.00%     0.00% 0.00%
Statute of limitations expiration   0.00%       0.00%
EffectiveIncomeTaxRateReconciliationPenalties   0.00%       0.00%
Effective Income Tax Rate Reconciliation, Tax Settlement, Other, Percent   0.00%     0.00% 0.00%
Fitzpatrick bargain purchase gain 0.00%       0.00%  
Like-kind exchange(a) [2]         0.00%  
Other (0.20%) 0.10%     (0.00%) (1.50%)
Effective income tax rate 20.00% 30.70%     20.40% 25.90%
Baltimore Gas and Electric Company [Member]            
Effective Income Tax Rate Reconciliation, Percent [Abstract]            
U.S. Federal statutory rate 35.00% 35.00%     35.00% 35.00%
Increase (decrease) due to:            
State income taxes, net of Federal income tax benefit 5.30% 5.20%     5.20% 4.80% [1]
Qualified nuclear decommissioning trust fund income (0.00%) (0.00%)     (0.00%) (0.00%)
Amortization of investment tax credit, including deferred taxes on basis difference (0.10%) (0.20%)     (0.10%) (0.20%)
Plant basis differences (0.80%) (0.50%)     (0.80%) (3.30%)
Production tax credits and other credits 0.00% 0.00%     0.00% 0.00%
Noncontrolling interests 0.00% 0.00%     0.00% 0.00%
Statute of limitations expiration   0.00%       0.00%
EffectiveIncomeTaxRateReconciliationPenalties   0.00%       0.00%
Effective Income Tax Rate Reconciliation, Tax Settlement, Other, Percent   0.00%     0.00% 0.00%
Fitzpatrick bargain purchase gain 0.00%       0.00%  
Like-kind exchange(a) [2]         0.00%  
Other (0.20%) (0.40%)     0.20% (0.00%)
Effective income tax rate 39.20% 39.10%     39.50% 36.30%
Potomac Electric Power Company [Member]            
Effective Income Tax Rate Reconciliation, Percent [Abstract]            
U.S. Federal statutory rate 35.00% 35.00%     35.00% 35.00%
Increase (decrease) due to:            
State income taxes, net of Federal income tax benefit 2.20% 5.60%     3.00% 23.00% [1]
Qualified nuclear decommissioning trust fund income (0.00%) (0.00%)     (0.00%) (0.00%)
Amortization of investment tax credit, including deferred taxes on basis difference (0.10%) (0.00%)     (0.10%) (0.20%)
Plant basis differences (6.70%) (6.70%)     (6.30%) (29.00%)
Production tax credits and other credits 0.00% 0.00%     0.00% 0.00%
Noncontrolling interests 0.00% 0.00%     0.00% 0.00%
Statute of limitations expiration   0.00%       0.00%
EffectiveIncomeTaxRateReconciliationPenalties   0.00%       0.00%
Effective Income Tax Rate Reconciliation, Tax Settlement, Other, Percent   (2.30%)     (8.00%) 36.70%
Fitzpatrick bargain purchase gain 0.00%       0.00%  
Like-kind exchange(a) [2]         0.00%  
Other (0.00%) (0.90%)     (0.30%) (2.50%)
Effective income tax rate 30.40% 30.70%     23.30% 63.00%
Delmarva Power and Light Company [Member]            
Effective Income Tax Rate Reconciliation, Percent [Abstract]            
U.S. Federal statutory rate 35.00% 35.00%     35.00% 35.00% [3]
Increase (decrease) due to:            
State income taxes, net of Federal income tax benefit 5.30% 5.20%     5.10% 310.50% [1],[3]
Qualified nuclear decommissioning trust fund income (0.00%) (0.00%)     (0.00%) (0.00%) [3]
Amortization of investment tax credit, including deferred taxes on basis difference (0.20%) (0.20%)     (0.20%) (17.90%) [3]
Plant basis differences (1.90%) (1.30%)     (1.80%) (98.60%) [3]
Production tax credits and other credits 0.00% 0.00%     0.00% 0.00% [3]
Noncontrolling interests 0.00% 0.00%     0.00% 0.00% [3]
Statute of limitations expiration   0.00%       0.00% [3]
EffectiveIncomeTaxRateReconciliationPenalties   0.00%       0.00% [3]
Effective Income Tax Rate Reconciliation, Tax Settlement, Other, Percent   (8.60%)     (10.00%) 635.90% [3]
Fitzpatrick bargain purchase gain 0.00%       0.00%  
Like-kind exchange(a) [2]         0.00%  
Other (0.20%) 0.10%     0.60% 35.10% [3]
Effective income tax rate 38.00% 30.20%     28.70% 900.00% [3]
Atlantic City Electric Company [Member]            
Effective Income Tax Rate Reconciliation, Percent [Abstract]            
U.S. Federal statutory rate 35.00% 35.00%     35.00% 35.00% [3]
Increase (decrease) due to:            
State income taxes, net of Federal income tax benefit 5.60% 6.10%     5.60% 5.50% [1],[3]
Qualified nuclear decommissioning trust fund income (0.00%) (0.00%)     (0.00%) (0.00%) [3]
Amortization of investment tax credit, including deferred taxes on basis difference (0.40%) (0.10%)     (0.40%) 0.50% [3]
Plant basis differences (3.40%) (4.60%)     (3.40%) 7.80% [3]
Production tax credits and other credits 0.00% 0.00%     0.00% 0.00% [3]
Noncontrolling interests 0.00% 0.00%     0.00% 0.00% [3]
Statute of limitations expiration   0.00%       0.00% [3]
EffectiveIncomeTaxRateReconciliationPenalties   0.00%       0.00% [3]
Effective Income Tax Rate Reconciliation, Tax Settlement, Other, Percent   (2.90%)     (23.00%) (35.40%) [3]
Fitzpatrick bargain purchase gain 0.00%       0.00%  
Like-kind exchange(a) [2]         0.00%  
Other 0.10% (0.60%)     (0.30%) 0.40% [3]
Effective income tax rate 36.90% 32.90%     13.50% 13.80% [3]
Pepco Holdings LLC [Member] | Successor [Member]            
Effective Income Tax Rate Reconciliation, Percent [Abstract]            
U.S. Federal statutory rate 35.00% 35.00%   35.00% 35.00%  
Increase (decrease) due to:            
State income taxes, net of Federal income tax benefit 5.10% 5.60%   4.40% [1] 4.90%  
Qualified nuclear decommissioning trust fund income (0.00%) (0.00%)   (0.00%) (0.00%)  
Amortization of investment tax credit, including deferred taxes on basis difference (0.20%) (0.10%)   0.50% (0.20%)  
Plant basis differences (4.90%) (5.00%)   17.50% (4.60%)  
Production tax credits and other credits 0.00% 0.00%   0.00% 0.00%  
Noncontrolling interests 0.00% 0.00%   0.00% 0.00%  
Statute of limitations expiration   0.00%   0.00%    
EffectiveIncomeTaxRateReconciliationPenalties   0.00%   0.00%    
Effective Income Tax Rate Reconciliation, Tax Settlement, Other, Percent   (5.70%)   (49.80%) (11.80%)  
Fitzpatrick bargain purchase gain 0.00%       0.00%  
Like-kind exchange(a) [2]         0.00%  
Other 0.20% (0.70%)   1.40% (0.00%)  
Effective income tax rate 35.20% 29.10%   9.00% 23.30%  
Pepco Holdings LLC [Member] | Predecessor [Member]            
Effective Income Tax Rate Reconciliation, Percent [Abstract]            
U.S. Federal statutory rate     35.00%      
Increase (decrease) due to:            
State income taxes, net of Federal income tax benefit [1]     11.90%      
Qualified nuclear decommissioning trust fund income     (0.00%)      
Amortization of investment tax credit, including deferred taxes on basis difference     (0.90%)      
Plant basis differences     (13.50%)      
Production tax credits and other credits     0.00%      
Noncontrolling interests     0.00%      
Statute of limitations expiration     0.00%      
EffectiveIncomeTaxRateReconciliationPenalties     0.00%      
Effective Income Tax Rate Reconciliation, Tax Settlement, Other, Percent     11.10%      
Other     3.60%      
Effective income tax rate     47.20%      
[1] Includes a remeasurement of uncertain state income tax positions for Pepco and DPL.
[2] See Like-Kind Exchange within the Other Income Tax Matters section below for further details.
[3] DPL and ACE recognized a loss before income taxes for the nine months ended September 30, 2016, and PHI recognized a loss before income taxes for the period of March 24, 2016, through September 30, 2016. As a result, positive percentages represent an income tax benefit for the periods presented.