Short-Term Borrowing - Additional Information (Detail) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2015
Short-term Debt [Line Items]
Commercial paper, outstanding	$ 1,199,000,000	$ 1,529,000,000
Weighted average interest rate (percent)	0.70%	0.70%
Loans outstanding under credit agreement	$ 0	$ 0
Letters of credit outstanding under the Credit Agreement	2,000,000	15,000,000
CECONY
Short-term Debt [Line Items]
Commercial paper, outstanding	520,000,000	$ 1,033,000,000
Weighted average interest rate (percent)		0.70%
Letters of credit outstanding under the Credit Agreement	$ 2,000,000