Summary of Significant Accounting Policies and Other Matters - Changes in Accumulated Other Comprehensive Income/(Loss) by Component (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
AOCI Attributable to Parent, Net of Tax [Roll Forward]
BALANCE AS OF BEGINNING OF PERIOD	$ 15,425	$ 14,306	$ 13,061
TOTAL OTHER COMPREHENSIVE INCOME, NET OF TAXES	10	1	7
BALANCE AS OF END OF PERIOD	16,839	15,425	14,306
Accumulated OCI
AOCI Attributable to Parent, Net of Tax [Roll Forward]
BALANCE AS OF BEGINNING OF PERIOD	(26)	(27)	(34)
TOTAL OTHER COMPREHENSIVE INCOME, NET OF TAXES	10	1	7
BALANCE AS OF END OF PERIOD	(16)	(26)	(27)
Pension Plan Liabilities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
OCI before reclassifications, net of tax	4	(4)	2
Amounts reclassified from accumulated OCI related to pension plan liabilities, net of tax	6	5	5
TOTAL OTHER COMPREHENSIVE INCOME, NET OF TAXES	10	1	7
OCI before reclassifications, tax	3	3	(1)
Amounts reclassified from accumulated OCI related to pension plan liabilities, tax	(2)	(3)	(3)
CECONY
AOCI Attributable to Parent, Net of Tax [Roll Forward]
TOTAL OTHER COMPREHENSIVE INCOME, NET OF TAXES	1	1	2
CECONY | Accumulated OCI
AOCI Attributable to Parent, Net of Tax [Roll Forward]
BALANCE AS OF BEGINNING OF PERIOD	(6)	(7)	(9)
TOTAL OTHER COMPREHENSIVE INCOME, NET OF TAXES	1	1	2
BALANCE AS OF END OF PERIOD	(5)	(6)	(7)
CECONY | Pension Plan Liabilities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
OCI before reclassifications, net of tax	0	0	1
Amounts reclassified from accumulated OCI related to pension plan liabilities, net of tax	1	1	1
TOTAL OTHER COMPREHENSIVE INCOME, NET OF TAXES	$ 1	1	2
OCI before reclassifications, tax		(1)	1
Amounts reclassified from accumulated OCI related to pension plan liabilities, tax		$ (1)	$ (1)