Capitalization - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Dec. 31, 2014
Schedule of Capitalization [Line Items]
Long-term debt, fair value	$ 14,224	$ 13,998
Level 2 [Member]
Schedule of Capitalization [Line Items]
Long-term debt, fair value	13,588
Level 3 [Member]
Schedule of Capitalization [Line Items]
Long-term debt, fair value	636
CECONY [Member]
Schedule of Capitalization [Line Items]
Long-term debt, fair value	13,066	12,846
CECONY [Member] | Level 2 [Member]
Schedule of Capitalization [Line Items]
Long-term debt, fair value	12,430
CECONY [Member] | Level 3 [Member]
Schedule of Capitalization [Line Items]
Long-term debt, fair value	636
Tax-exempt debt	$ 636