Summary of Significant Accounting Policies and Other Matters - Utility Plant (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Finite-Lived Intangible Assets [Line Items]
Accumulated amortization	$ 53	$ 29
Software Licenses
Finite-Lived Intangible Assets [Line Items]
Gross asset	98	100
Estimated aggregate annual amortization expense	7
Accumulated amortization	5	3
CECONY | Software Licenses
Finite-Lived Intangible Assets [Line Items]
Gross asset	93	95
Estimated aggregate annual amortization expense	7
Accumulated amortization	$ 5	$ 3