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, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	$ 18,441	$ 18,467	$ 18,213	$ 17,865	$ 17,501	$ 16,839	$ 18,213	$ 16,839
Beginning Balance			18,022				18,022
TOTAL OTHER COMPREHENSIVE INCOME, NET OF TAXES	2	0	5	1	1	4	7	6
Ending Balance	18,711	18,441	18,467	18,134	17,865	17,501	18,711	18,134
Ending Balance	18,494						18,494
Accumulated OCI
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(14)	(14)	(19)	(11)	(12)	(16)	(19)	(16)
TOTAL OTHER COMPREHENSIVE INCOME, NET OF TAXES	2		5	1	1	4
Ending Balance	(12)	(14)	(14)	(10)	(11)	(12)	(12)	(10)
Pension Plan LIabilities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
OCI before reclassifications, net of tax of $(1) for Con Edison in 2020 and 2019							4	2
Amounts reclassified from accumulated OCI related to pension plan liabilities, net of tax of for Con Edison	2			1			3	4
TOTAL OTHER COMPREHENSIVE INCOME, NET OF TAXES	2			1			7	6
OCI before reclassifications, tax							(1)	(1)
CECONY
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	14,265	14,333	14,147	13,868	13,319	12,910	14,147	12,910
TOTAL OTHER COMPREHENSIVE INCOME, NET OF TAXES	0	1	1	1	0	0	2	1
Ending Balance	14,575	14,265	14,333	14,079	13,868	13,319	14,575	14,079
CECONY | Pension Plan LIabilities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Amounts reclassified from accumulated OCI related to pension plan liabilities, tax	(1)			(1)			(2)	(1)
CECONY | Accumulated OCI
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(4)	(5)	(6)	(5)	(5)	(5)	(6)	(5)
TOTAL OTHER COMPREHENSIVE INCOME, NET OF TAXES	0	1	1	1
Ending Balance	(4)	$ (4)	$ (5)	(4)	$ (5)	$ (5)	(4)	(4)
CECONY | Pension Plan Liabilities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
OCI before reclassifications, net of tax of $(1) for Con Edison in 2020 and 2019							0	0
Amounts reclassified from accumulated OCI related to pension plan liabilities, net of tax of for Con Edison	0			1			2	1
TOTAL OTHER COMPREHENSIVE INCOME, NET OF TAXES	$ 0			$ 1			$ 2	$ 1