Short-Term Borrowing - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2014	Dec. 31, 2013
Short-term Debt [Line Items]
Commercial paper, outstanding	$ 830	$ 1,451
Weighted average interest rate	0.20%	0.20%
Loans outstanding under the credit agreement	0	0
Letters of credit outstanding under the credit agreement	56	26
CECONY [Member]
Short-term Debt [Line Items]
Commercial paper, outstanding	669	1,210
Weighted average interest rate	0.20%	0.20%
Letters of credit outstanding under the credit agreement	$ 11	$ 11