Other Material Contingencies - Additional Information (Detail)		1 Months Ended	9 Months Ended
	Mar. 12, 2014 building Person	Jul. 31, 2007 Person	Sep. 30, 2016 USD ($) lawsuit	Dec. 31, 2015 USD ($)	Dec. 31, 2014
Guarantor Obligations [Line Items]
Guarantee obligations maximum exposure			$ 2,422,000,000	$ 2,856,000,000
Ownership interest, percentage					45.70%
Estimated project cost percentage			175.00%
Manhattan Steam Main Rupture
Guarantor Obligations [Line Items]
Number of person died in steam ruptured | Person		1
Number of suits pending against the company | lawsuit			60
Estimated accrued liability for suits			$ 30,000,000
Insurance receivable			$ 39,000,000
Manhattan Explosion and Fire
Guarantor Obligations [Line Items]
Number of suits pending against the company | lawsuit			70
Number of buildings destroyed by fire | building	2
Number of people died in explosion and fire incident | Person	8
Number of people injured in explosion and fire incident | Person	50
Financial And Performance Guarantee For CET Gas
Guarantor Obligations [Line Items]
Guarantee obligations maximum exposure			$ 25,000,000
Financial And Performance Guarantee During Period in which Con Edison Solutions Provides Transition Services
Guarantor Obligations [Line Items]
Guarantee obligations maximum exposure			123,000,000
Financial and Performance Guarantee, Other
Guarantor Obligations [Line Items]
Guarantee obligations maximum exposure			128,000,000
Indemnity agreements amount			70,000,000
Electric provider obligation to Public Utility Commission of Texas			5,000,000
Finance and Performance Guarantee for Consolidated Edison Solutions
Guarantor Obligations [Line Items]
Guarantee obligations maximum exposure			$ 53,000,000