Summary of Significant Accounting Policies and Other Matters - Investments (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Schedule of Equity Method Investments [Line Items]
Supplemental retirement income plan assets	$ 397	$ 326
Deferred income plan assets	81	75
Other	2	2
Total investments	2,065	1,766
CET | Stagecoach Gas Services, LLC
Schedule of Equity Method Investments [Line Items]
Equity method investments	924	948
CET | Mountain Valley Pipeline LLC
Schedule of Equity Method Investments [Line Items]
Equity method investments	602	363
CET | New York Transco, LLC
Schedule of Equity Method Investments [Line Items]
Equity method investments	59	52
CECONY
Schedule of Equity Method Investments [Line Items]
Supplemental retirement income plan assets	371	301
Deferred income plan assets	81	75
Other	9	9
Total investments	461	385
CECONY | CET | Stagecoach Gas Services, LLC
Schedule of Equity Method Investments [Line Items]
Equity method investments	0	0
CECONY | CET | Mountain Valley Pipeline LLC
Schedule of Equity Method Investments [Line Items]
Equity method investments	0	0
CECONY | CET | New York Transco, LLC
Schedule of Equity Method Investments [Line Items]
Equity method investments	$ 0	$ 0