Summary of Significant Accounting Policies and Other Matters - Utility Plant (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Finite-Lived Intangible Assets [Line Items]
Accumulated amortization	$ 254	$ 228
Other deferred charges and noncurrent assets	57	54
Prepayments	14	12
Depreciation expense	3
Accumulated depreciation	12	10
Software Licenses
Finite-Lived Intangible Assets [Line Items]
Gross asset	84	86
Estimated aggregate annual amortization expense	7
Accumulated amortization	19	17
CECONY
Finite-Lived Intangible Assets [Line Items]
Other deferred charges and noncurrent assets	54	51
Prepayments	13	11
Depreciation expense	3
Accumulated depreciation	11	8
CECONY | Software Licenses
Finite-Lived Intangible Assets [Line Items]
Gross asset	80	81
Estimated aggregate annual amortization expense	7
Accumulated amortization	$ 18	$ 17