Summary of Significant Accounting Policies and Other Matters - Utility Plant (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Finite-Lived Intangible Assets [Line Items]
Accumulated amortization	$ 203	$ 126
Software Licenses
Finite-Lived Intangible Assets [Line Items]
Gross asset	88	93
Estimated aggregate annual amortization expense	7
Accumulated amortization	15	10
CECONY | Software Licenses
Finite-Lived Intangible Assets [Line Items]
Gross asset	83	88
Estimated aggregate annual amortization expense	7
Accumulated amortization	$ 15	$ 10