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, 2020	Dec. 31, 2019	Dec. 31, 2018
AOCI Attributable to Parent, Net of Tax [Roll Forward]
BALANCE AS OF BEGINNING OF PERIOD	$ 18,213	$ 16,839	$ 15,425
BALANCE AS OF BEGINNING OF PERIOD	18,022
TOTAL OTHER COMPREHENSIVE INCOME (LOSS), NET OF TAXES	(6)	(3)	10
BALANCE AS OF END OF PERIOD	18,847	18,022
BALANCE AS OF END OF PERIOD	19,065	18,213	16,839
Accumulated OCI
AOCI Attributable to Parent, Net of Tax [Roll Forward]
BALANCE AS OF BEGINNING OF PERIOD	(19)	(16)	(26)
BALANCE AS OF END OF PERIOD	(25)	(19)	(16)
Pension Plan Liabilities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
OCI before reclassifications, net of tax	(11)	(10)	4
Amounts reclassified from accumulated OCI related to pension plan liabilities, net of tax	5	7	6
TOTAL OTHER COMPREHENSIVE INCOME (LOSS), NET OF TAXES	(6)	(3)	10
OCI before reclassifications, tax	4	(6)	3
Amounts reclassified from accumulated OCI related to pension plan liabilities, tax	(2)	(2)	(2)
Accumulated OCI
AOCI Attributable to Parent, Net of Tax [Roll Forward]
BALANCE AS OF BEGINNING OF PERIOD	(19)	(16)	(26)
TOTAL OTHER COMPREHENSIVE INCOME (LOSS), NET OF TAXES	(6)	(3)	10
BALANCE AS OF END OF PERIOD	(25)	(19)	(16)
CECONY
AOCI Attributable to Parent, Net of Tax [Roll Forward]
BALANCE AS OF BEGINNING OF PERIOD	14,147	12,910	12,439
TOTAL OTHER COMPREHENSIVE INCOME (LOSS), NET OF TAXES	(1)	(1)	1
BALANCE AS OF END OF PERIOD	14,849	14,147	12,910
CECONY | Accumulated OCI
AOCI Attributable to Parent, Net of Tax [Roll Forward]
BALANCE AS OF BEGINNING OF PERIOD	(6)	(5)	(6)
TOTAL OTHER COMPREHENSIVE INCOME (LOSS), NET OF TAXES	(1)	(1)	1
BALANCE AS OF END OF PERIOD	(7)	(6)	(5)
CECONY | Pension Plan Liabilities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
OCI before reclassifications, net of tax	(3)	(3)	0
Amounts reclassified from accumulated OCI related to pension plan liabilities, net of tax	2	2	1
TOTAL OTHER COMPREHENSIVE INCOME (LOSS), NET OF TAXES	(1)	(1)	$ 1
OCI before reclassifications, tax	$ 1	$ (1)