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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

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