Summary of Significant Accounting Policies and Other Matters - Changes in Accumulated Other Comprehensive Income/(Loss) (Details) - USD ($) $ in Millions	3 Months Ended						9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	$ 20,053	$ 19,282	$ 19,065	$ 18,441	$ 18,467	$ 18,213	$ 19,065	$ 18,213
Beginning Balance			18,847				18,847
TOTAL OTHER COMPREHENSIVE INCOME, NET OF TAXES	2	2	4	2		5	8	7
Ending Balance	20,377	20,053	19,282	18,711	18,441	18,467	20,377	18,711
Ending Balance	20,037						20,037
Subsidiaries
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	15,924	15,192	14,849	14,265	14,333	14,147	14,849	14,147
TOTAL OTHER COMPREHENSIVE INCOME, NET OF TAXES					1	1
Ending Balance	16,220	15,924	15,192		14,265	14,333	16,220
Accumulated OCI
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(19)		(25)	(14)		(19)	(25)	(19)
TOTAL OTHER COMPREHENSIVE INCOME, NET OF TAXES				2
Ending Balance	(17)	(19)		(12)	(14)		(17)	(12)
Pension Plan LIabilities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
OCI before reclassifications, net of tax							2	4
Amounts reclassified from accumulated OCI related to pension plan liabilities, net of tax	2			2			6	3
TOTAL OTHER COMPREHENSIVE INCOME, NET OF TAXES	2			2			8	7
OCI before reclassifications, tax							(1)
Amounts reclassified from accumulated OCI related to pension plan liabilities, tax	(1)			(1)			(1)	(1)
Accumulated OCI
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(19)	(21)	(25)		(14)	(19)	(25)	(19)
TOTAL OTHER COMPREHENSIVE INCOME, NET OF TAXES	2	2	4			5
Ending Balance	(17)	(19)	(21)			(14)	(17)
Accumulated OCI | Subsidiaries
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(7)	(7)	(7)	(4)	(5)	(6)	(7)	(6)
TOTAL OTHER COMPREHENSIVE INCOME, NET OF TAXES					1	1
Ending Balance	(7)	$ (7)	$ (7)	(4)	$ (4)	$ (5)	(7)	(4)
Pension Plan Liabilities | Subsidiaries
AOCI Attributable to Parent, Net of Tax [Roll Forward]
OCI before reclassifications, net of tax							0	0
Amounts reclassified from accumulated OCI related to pension plan liabilities, net of tax	0			0			0	2
TOTAL OTHER COMPREHENSIVE INCOME, NET OF TAXES	$ 0			0			0	2
CECONY
AOCI Attributable to Parent, Net of Tax [Roll Forward]
TOTAL OTHER COMPREHENSIVE INCOME, NET OF TAXES				0
Ending Balance				14,575				14,575
CECONY | Pension Plan LIabilities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Amounts reclassified from accumulated OCI related to pension plan liabilities, tax							$ (2)
CECONY | Accumulated OCI
AOCI Attributable to Parent, Net of Tax [Roll Forward]
TOTAL OTHER COMPREHENSIVE INCOME, NET OF TAXES				0
Ending Balance				$ (4)				$ (4)