Stock-Based Compensation - Stock-Based Compensation Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 14	$ 63	$ 50
Income tax benefit	4	25	20
Performance-based restricted stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	3	53	42
Time-based restricted stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	2	2	2
Non-employee director deferred stock compensation
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	3	2	2
Stock purchase plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	6	6	4
CECONY
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	13	55	44
Income tax benefit	4	22	18
CECONY | Performance-based restricted stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	3	45	36
CECONY | Time-based restricted stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	1	2	2
CECONY | Non-employee director deferred stock compensation
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	3	2	2
CECONY | Stock purchase plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 6	$ 6	$ 4