Goodwill and Other Intangible Assets (Details)	12 Months Ended
	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($) business_acquisition	Dec. 31, 2015 USD ($)
Goodwill [Line Items]
Goodwill	$ 428,000,000	$ 428,000,000
Impairment charge	0
Finite lived intangible assets, accumulated amortization	15,000,000	6,000,000
Amortization expense	9,000,000	2,000,000	$ 0
Intangibles Future Amortization:
Year 1	9,000,000
Year 2	9,000,000
Year 3	9,000,000
Year 4	9,000,000
Year 5	9,000,000
Other Intangible Assets
Goodwill [Line Items]
Finite lived intangible assets, net	0	5,000,000
Finite lived intangible assets, accumulated amortization	6,000,000	5,000,000
CECONY
Goodwill [Line Items]
Goodwill	245,000,000	245,000,000
CECONY | Other Intangible Assets
Goodwill [Line Items]
Finite lived intangible assets, net	0	0
O&R
Goodwill [Line Items]
Goodwill	161,000,000	161,000,000
O&R Merger
Goodwill [Line Items]
Goodwill	406,000,000	406,000,000
Gas Storage Company | CET Gas
Goodwill [Line Items]
Goodwill	8,000,000	8,000,000
Energy Services Company | Clean Energy Businesses
Goodwill [Line Items]
Goodwill		$ 15,000,000
Number of businesses acquired included in goodwill impairment test | business_acquisition		2
Impairment charge		$ 15,000,000
Impairment charge, net of tax		12,000,000
Residential Solar Company | Clean Energy Businesses
Goodwill [Line Items]
Goodwill		14,000,000
Power Purchase
Goodwill [Line Items]
Finite lived intangible assets, net	131,000,000	119,000,000
Finite lived intangible assets, accumulated amortization	$ 9,000,000	$ 1,000,000