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, 2019	Dec. 31, 2018	Dec. 31, 2017
AOCI Attributable to Parent, Net of Tax [Roll Forward]
BALANCE AS OF BEGINNING OF PERIOD	$ 16,839	$ 15,425	$ 14,306
TOTAL OTHER COMPREHENSIVE INCOME, NET OF TAXES	(3)	10	1
BALANCE AS OF END OF PERIOD	18,213	16,839	15,425
Accumulated OCI
AOCI Attributable to Parent, Net of Tax [Roll Forward]
BALANCE AS OF BEGINNING OF PERIOD	(16)	(26)	(27)
TOTAL OTHER COMPREHENSIVE INCOME, NET OF TAXES	(3)	10	1
BALANCE AS OF END OF PERIOD	(19)	(16)	(26)
Pension Plan Liabilities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
OCI before reclassifications, net of tax	(10)	4	(4)
Amounts reclassified from accumulated OCI related to pension plan liabilities, net of tax	7	6	5
TOTAL OTHER COMPREHENSIVE INCOME, NET OF TAXES	(3)	10	1
OCI before reclassifications, tax	(6)	3	3
Amounts reclassified from accumulated OCI related to pension plan liabilities, tax	(2)	(2)	(3)
CECONY
AOCI Attributable to Parent, Net of Tax [Roll Forward]
TOTAL OTHER COMPREHENSIVE INCOME, NET OF TAXES	(1)	1	1
CECONY | Accumulated OCI
AOCI Attributable to Parent, Net of Tax [Roll Forward]
BALANCE AS OF BEGINNING OF PERIOD	(5)	(6)	(7)
TOTAL OTHER COMPREHENSIVE INCOME, NET OF TAXES	(1)	1	1
BALANCE AS OF END OF PERIOD	(6)	(5)	(6)
CECONY | Pension Plan Liabilities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
OCI before reclassifications, net of tax	(3)	0	0
Amounts reclassified from accumulated OCI related to pension plan liabilities, net of tax	2	1	1
TOTAL OTHER COMPREHENSIVE INCOME, NET OF TAXES	(1)	$ 1	1
OCI before reclassifications, tax	$ (1)		1
Amounts reclassified from accumulated OCI related to pension plan liabilities, tax			$ (1)