Shareholders' Equity Shareholder Narrative (Details) - USD ($) $ / shares in Units, $ in Millions						12 Months Ended
	Jun. 01, 2017	Sep. 19, 2016	Sep. 18, 2016	Jul. 03, 2016	Jul. 03, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jun. 30, 2017	Jul. 30, 2015	Jun. 30, 2014
Schedule of Capitalization, Equity [Line Items]
Stock Repurchased During Period, Shares							33,000,000	0
Temporary Equity, Share Subscriptions										57,500,000	57,500,000
Sale of Stock, Price Per Share										$ 32.48
Treasury Stock, Number of Shares Held						2,000,000	2,000,000
Treasury stock, at cost						$ 123	$ 123
Stock Repurchased During Period, Value						$ 0		$ 0
Stock Redeemed or Called During Period, Value								(193)
Preferred Stock [Member]
Schedule of Capitalization, Equity [Line Items]
Preferred Stock, Shares Authorized						100,000,000	100,000,000
Preferred Stock, Shares Outstanding						0	0
Equity units issued [Member]
Schedule of Capitalization, Equity [Line Items]
Stock Issued During Period, Shares, Treasury Stock Reissued	33,000,000
Minimum [Member]
Schedule of Capitalization, Equity [Line Items]
Forward Contract Indexed to Issuer's Equity, Settlement Alternatives, Cash, at Fair Value										$ 1,870
Commonwealth Edison Co [Member]
Schedule of Capitalization, Equity [Line Items]
Class of Warrant or Right, Outstanding						60,285	60,584
Commonwealth Edison Co [Member] | Common Stock [Member]
Schedule of Capitalization, Equity [Line Items]
Common Stock Shares Reserved For Warrant Conversion						20,095	20,195
Commonwealth Edison Co [Member] | Preferred Stock [Member]
Schedule of Capitalization, Equity [Line Items]
Preferred Stock, Shares Authorized						850,000	850,000
Preferred Stock, Shares Outstanding						0	0
Commonwealth Edison Co [Member] | Cumulative Preferred Stock [Member]
Schedule of Capitalization, Equity [Line Items]
Preferred Stock, Shares Authorized						6,810,451	6,810,451
Preferred Stock, Shares Outstanding						0	0
Baltimore Gas and Electric Company [Member]
Schedule of Capitalization, Equity [Line Items]
Preferred Stock, Value, Outstanding								$ 190
Preferred Stock, Redemption Price Per Share								$ 100
Stock Redeemed or Called During Period, Shares		400,000	500,000	400,000	600,000
Preferred Stock, Dividend Rate, Percentage		6.70%	6.97%	7.125%	6.99%
Stock Redeemed or Called During Period, Value			$ 90	$ 100				$ (190)
Junior Subordinated Debt [Member]
Schedule of Capitalization, Equity [Line Items]
Shares Issued, Price Per Share									$ 35
Junior Subordinated Notes							$ 1,150				$ 1,150
Equity units issued											23,000,000
Stock Issued During Period, Shares, Treasury Stock Reissued							33,000,000