Fair Value Measurements - Reconciliation of Beginning and Ending Net Balances for Assets and Liabilities Measured at Level 3 Fair Value (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 1	$ 6
Included in earnings	0	(7)
Included in regulatory assets and liabilities	2	(3)
Settlements	0	0
Ending balance	3	(4)
CECONY
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	1	8
Included in earnings	0	(1)
Included in regulatory assets and liabilities	0	(4)
Settlements	0	(1)
Ending balance	$ 1	$ 2