Summary of Significant Accounting Policies and Other Matters - Utility Plant (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Finite-Lived Intangible Assets [Line Items]
Accumulated amortization	$ 152	$ 126
Software Licenses
Finite-Lived Intangible Assets [Line Items]
Gross asset	91	93
Accumulated amortization	12	10
CECONY | Software Licenses
Finite-Lived Intangible Assets [Line Items]
Gross asset	87	88
Estimated aggregate annual amortization expense	7
Accumulated amortization	$ 11	$ 10