Environmental Matters - Environmental Remediation Costs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Environmental Exit Cost [Line Items]
Remediation costs incurred	$ 34	$ 37
Insurance recoveries received	1	0
CECONY
Environmental Exit Cost [Line Items]
Remediation costs incurred	21	34
Insurance recoveries received	$ 1	$ 0