Capitalization - Common Stock (Details) - USD ($) $ in Millions	1 Months Ended			12 Months Ended
	Dec. 31, 2020	Jan. 31, 2020	Jun. 30, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	May 31, 2019	Dec. 31, 2017
Schedule of Capitalization [Line Items]
Common stock, shares authorized (in shares)	500,000,000			500,000,000
Common stock, shares outstanding (in shares)	342,297,534			342,297,534	332,629,597
Treasury shares (in shares)	23,210,700			23,210,700	23,210,700
Value of shares issued				$ 640	$ 825	$ 705
Proceeds from issuance of common stock				$ 640	$ 825	$ 705
0.65 Percent Debentures Due 2023 | Debentures
Schedule of Capitalization [Line Items]
Interest rate	0.65%			0.65%
Proceeds from sale of aggregate principal amount	$ 650
Term Loan Due July 2020 | Term Loan
Schedule of Capitalization [Line Items]
Repayments of debt	$ 820
Common Stock
Schedule of Capitalization [Line Items]
Common stock, shares outstanding (in shares)	342,000,000			342,000,000	333,000,000	321,000,000		310,000,000
Shares issued (in shares)	7,200,000			9,000,000	12,000,000	11,000,000
Value of shares issued				$ 1	$ 1
Proceeds from issuance of common stock	$ 553
Forward Contract | Common Stock
Schedule of Capitalization [Line Items]
Common stock, shares subject to forward sale agreements (in shares)							5,800,000
Shares issued (in shares)		1,050,000	4,750,000
Value of shares issued		$ 88	$ 400
CECONY
Schedule of Capitalization [Line Items]
Common stock, shares authorized (in shares)	340,000,000			340,000,000
Common stock, shares outstanding (in shares)	235,488,094			235,488,094	235,488,094
Treasury shares (in shares)	21,976,200			21,976,200	21,976,200
CECONY | Common Stock
Schedule of Capitalization [Line Items]
Common stock, shares outstanding (in shares)	235,000,000			235,000,000	235,000,000	235,000,000		235,000,000