Summary of Significant Accounting Policies and Other Matters - Investments (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Schedule of Equity Method Investments [Line Items]
Equity method investments	$ 0	$ 467
Supplemental retirement income plan assets	326	330
Deferred income plan assets	75	73
Other	2	9
Total investments	1,766	2,001
CET | Stagecoach Gas Services, LLC
Schedule of Equity Method Investments [Line Items]
Equity method investments	948	971
CET | Mountain Valley Pipeline LLC
Schedule of Equity Method Investments [Line Items]
Equity method investments	363	98
CET | New York Transco, LLC
Schedule of Equity Method Investments [Line Items]
Equity method investments	52	53
CECONY
Schedule of Equity Method Investments [Line Items]
Equity method investments	0	0
Supplemental retirement income plan assets	301	301
Deferred income plan assets	75	73
Other	9	9
Total investments	385	383
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