Environmental Matters - Accrued Liabilities and Regulatory Assets (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Site Contingency [Line Items]
Accrued liabilities	$ 841	$ 857
Regulatory assets	6,108	6,461
Subsidiaries
Site Contingency [Line Items]
Accrued liabilities	765	780
Manufactured gas plant sites
Site Contingency [Line Items]
Accrued liabilities	737	752
Other Superfund Sites
Site Contingency [Line Items]
Accrued liabilities	104	105
Superfund Sites
Site Contingency [Line Items]
Accrued liabilities	841	857
Regulatory assets	846	865
CECONY | Subsidiaries
Site Contingency [Line Items]
Regulatory assets	5,660	5,989
CECONY | Manufactured gas plant sites | Subsidiaries
Site Contingency [Line Items]
Accrued liabilities	662	676
CECONY | Other Superfund Sites | Subsidiaries
Site Contingency [Line Items]
Accrued liabilities	103	104
CECONY | Superfund Sites | Subsidiaries
Site Contingency [Line Items]
Accrued liabilities	765	780
Regulatory assets	$ 780	$ 791