Regulatory Matters Regulatory Matters - Schedule of Regulatory Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Regulatory Liabilities [Line Items]
Regulatory Liabilities	$ 10,388	$ 4,789
Regulatory Liability, Current	523	602
Noncurrent regulatory liabilities	9,865	4,187
Pension and other postretirement benefits
Regulatory Liabilities [Line Items]
Regulatory Liabilities	30	47
Deferred income taxes
Regulatory Liabilities [Line Items]
Regulatory Liabilities	5,241
Nuclear decommissioning
Regulatory Liabilities [Line Items]
Regulatory Liabilities	3,064	2,607
Removal costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	1,573	1,601
Deferred rent
Regulatory Liabilities [Line Items]
Regulatory Liabilities	36	39
Energy efficiency and demand response programs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	23	185
DLC program costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	7	8
Electric distribution tax repairs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	35	76
Gas distribution tax repairs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	9	20
Energy and transmission programs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	111	134
Renewable portfolio standards costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	63
Zero emission credit costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	112
Under-recovered uncollectible accounts
Regulatory Liabilities [Line Items]
Regulatory Liabilities	2
Other
Regulatory Liabilities [Line Items]
Regulatory Liabilities	82	72
Commonwealth Edison Co [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	6,577	3,698
Regulatory Liability, Current	249	329
Noncurrent regulatory liabilities	6,328	3,369
Commonwealth Edison Co [Member] | Pension and other postretirement benefits
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Commonwealth Edison Co [Member] | Deferred income taxes
Regulatory Liabilities [Line Items]
Regulatory Liabilities	2,479
Commonwealth Edison Co [Member] | Nuclear decommissioning
Regulatory Liabilities [Line Items]
Regulatory Liabilities	2,528	2,169
Commonwealth Edison Co [Member] | Removal costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	1,338	1,324
Commonwealth Edison Co [Member] | Deferred rent
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Commonwealth Edison Co [Member] | Energy efficiency and demand response programs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	4	141
Commonwealth Edison Co [Member] | DLC program costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Commonwealth Edison Co [Member] | Electric distribution tax repairs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Commonwealth Edison Co [Member] | Gas distribution tax repairs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Commonwealth Edison Co [Member] | Energy and transmission programs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	47	60
Commonwealth Edison Co [Member] | Renewable portfolio standards costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	63
Regulatory Liability, Current	10
Noncurrent regulatory liabilities	20
Commonwealth Edison Co [Member] | Zero emission credit costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	112
Commonwealth Edison Co [Member] | Under-recovered uncollectible accounts
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0
Commonwealth Edison Co [Member] | Other
Regulatory Liabilities [Line Items]
Regulatory Liabilities	6	4
PECO Energy Co [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	690	644
Regulatory Liability, Current	141	127
Noncurrent regulatory liabilities	549	517
PECO Energy Co [Member] | Pension and other postretirement benefits
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
PECO Energy Co [Member] | Deferred income taxes
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0
PECO Energy Co [Member] | Nuclear decommissioning
Regulatory Liabilities [Line Items]
Regulatory Liabilities	536	438
PECO Energy Co [Member] | Removal costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
PECO Energy Co [Member] | Deferred rent
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
PECO Energy Co [Member] | Energy efficiency and demand response programs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	19	41
PECO Energy Co [Member] | DLC program costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	7	8
PECO Energy Co [Member] | Electric distribution tax repairs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	35	76
PECO Energy Co [Member] | Gas distribution tax repairs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	9	20
PECO Energy Co [Member] | Energy and transmission programs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	60	56
PECO Energy Co [Member] | Renewable portfolio standards costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0
PECO Energy Co [Member] | Zero emission credit costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0
PECO Energy Co [Member] | Under-recovered uncollectible accounts
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0
PECO Energy Co [Member] | Other
Regulatory Liabilities [Line Items]
Regulatory Liabilities	24	5
Baltimore Gas and Electric Company [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	1,163	160
Regulatory Liability, Current	62	50
Noncurrent regulatory liabilities	1,101	110
Baltimore Gas and Electric Company [Member] | Pension and other postretirement benefits
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Baltimore Gas and Electric Company [Member] | Deferred income taxes
Regulatory Liabilities [Line Items]
Regulatory Liabilities	1,032
Baltimore Gas and Electric Company [Member] | Nuclear decommissioning
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Baltimore Gas and Electric Company [Member] | Removal costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	105	141
Baltimore Gas and Electric Company [Member] | Deferred rent
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Baltimore Gas and Electric Company [Member] | Energy efficiency and demand response programs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Baltimore Gas and Electric Company [Member] | DLC program costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Baltimore Gas and Electric Company [Member] | Electric distribution tax repairs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Baltimore Gas and Electric Company [Member] | Gas distribution tax repairs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Baltimore Gas and Electric Company [Member] | Energy and transmission programs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Baltimore Gas and Electric Company [Member] | Renewable portfolio standards costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0
Baltimore Gas and Electric Company [Member] | Zero emission credit costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0
Baltimore Gas and Electric Company [Member] | Under-recovered uncollectible accounts
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0
Baltimore Gas and Electric Company [Member] | Other
Regulatory Liabilities [Line Items]
Regulatory Liabilities	26	19
Pepco Holdings LLC [Member] | Successor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	1,928	237
Regulatory Liability, Current	56	79
Noncurrent regulatory liabilities	1,872	158
Pepco Holdings LLC [Member] | Pension and other postretirement benefits | Successor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Pepco Holdings LLC [Member] | Deferred income taxes | Successor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	1,730
Pepco Holdings LLC [Member] | Nuclear decommissioning | Successor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Pepco Holdings LLC [Member] | Removal costs | Successor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	130	136
Pepco Holdings LLC [Member] | Deferred rent | Successor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	36	39
Pepco Holdings LLC [Member] | Energy efficiency and demand response programs | Successor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	3
Pepco Holdings LLC [Member] | DLC program costs | Successor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Pepco Holdings LLC [Member] | Electric distribution tax repairs | Successor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Pepco Holdings LLC [Member] | Gas distribution tax repairs | Successor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Pepco Holdings LLC [Member] | Energy and transmission programs | Successor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	4	18
Pepco Holdings LLC [Member] | Renewable portfolio standards costs | Successor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0
Pepco Holdings LLC [Member] | Zero emission credit costs | Successor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0
Pepco Holdings LLC [Member] | Under-recovered uncollectible accounts | Successor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	2
Pepco Holdings LLC [Member] | Other | Successor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	26	41
Potomac Electric Power Company [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	832	31
Regulatory Liability, Current	3	11
Noncurrent regulatory liabilities	829	20
Potomac Electric Power Company [Member] | Pension and other postretirement benefits
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Potomac Electric Power Company [Member] | Deferred income taxes
Regulatory Liabilities [Line Items]
Regulatory Liabilities	809
Potomac Electric Power Company [Member] | Nuclear decommissioning
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Potomac Electric Power Company [Member] | Removal costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	20	18
Potomac Electric Power Company [Member] | Deferred rent
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Potomac Electric Power Company [Member] | Energy efficiency and demand response programs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	3
Potomac Electric Power Company [Member] | DLC program costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Potomac Electric Power Company [Member] | Electric distribution tax repairs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Potomac Electric Power Company [Member] | Gas distribution tax repairs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Potomac Electric Power Company [Member] | Energy and transmission programs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	8
Potomac Electric Power Company [Member] | Renewable portfolio standards costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0
Potomac Electric Power Company [Member] | Zero emission credit costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0
Potomac Electric Power Company [Member] | Under-recovered uncollectible accounts
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0
Potomac Electric Power Company [Member] | Other
Regulatory Liabilities [Line Items]
Regulatory Liabilities	3	2
Delmarva Power and Light Company [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	635	140
Regulatory Liability, Current	42	43
Noncurrent regulatory liabilities	593	97
Delmarva Power and Light Company [Member] | Pension and other postretirement benefits
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Delmarva Power and Light Company [Member] | Deferred income taxes
Regulatory Liabilities [Line Items]
Regulatory Liabilities	510
Delmarva Power and Light Company [Member] | Nuclear decommissioning
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Delmarva Power and Light Company [Member] | Removal costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	110	118
Delmarva Power and Light Company [Member] | Deferred rent
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Delmarva Power and Light Company [Member] | Energy efficiency and demand response programs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Delmarva Power and Light Company [Member] | DLC program costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Delmarva Power and Light Company [Member] | Electric distribution tax repairs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Delmarva Power and Light Company [Member] | Gas distribution tax repairs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Delmarva Power and Light Company [Member] | Energy and transmission programs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	1	5
Delmarva Power and Light Company [Member] | Renewable portfolio standards costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0
Delmarva Power and Light Company [Member] | Zero emission credit costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0
Delmarva Power and Light Company [Member] | Under-recovered uncollectible accounts
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0
Delmarva Power and Light Company [Member] | Other
Regulatory Liabilities [Line Items]
Regulatory Liabilities	14	17
Atlantic City Electric Company [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	422	25
Regulatory Liability, Current	11	25
Noncurrent regulatory liabilities	411	0
Atlantic City Electric Company [Member] | Pension and other postretirement benefits
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Atlantic City Electric Company [Member] | Deferred income taxes
Regulatory Liabilities [Line Items]
Regulatory Liabilities	411
Atlantic City Electric Company [Member] | Nuclear decommissioning
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Atlantic City Electric Company [Member] | Removal costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Atlantic City Electric Company [Member] | Deferred rent
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Atlantic City Electric Company [Member] | Energy efficiency and demand response programs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Atlantic City Electric Company [Member] | DLC program costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Atlantic City Electric Company [Member] | Electric distribution tax repairs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Atlantic City Electric Company [Member] | Gas distribution tax repairs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Atlantic City Electric Company [Member] | Energy and transmission programs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	3	5
Atlantic City Electric Company [Member] | Renewable portfolio standards costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0
Atlantic City Electric Company [Member] | Zero emission credit costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0
Atlantic City Electric Company [Member] | Under-recovered uncollectible accounts
Regulatory Liabilities [Line Items]
Regulatory Liabilities	2
Atlantic City Electric Company [Member] | Other
Regulatory Liabilities [Line Items]
Regulatory Liabilities	$ 6	$ 20