Environmental Matters - Accrued Liabilities and Regulatory Assets (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Site Contingency [Line Items]
Accrued liabilities	$ 847	$ 857
Regulatory assets	6,073	6,461
Subsidiaries
Site Contingency [Line Items]
Accrued liabilities	770	780
Manufactured gas plant sites
Site Contingency [Line Items]
Accrued liabilities	742	752
Other Superfund Sites
Site Contingency [Line Items]
Accrued liabilities	105	105
Superfund Sites
Site Contingency [Line Items]
Accrued liabilities	847	857
Regulatory assets	852	865
CECONY | Subsidiaries
Site Contingency [Line Items]
Regulatory assets	5,639	5,989
CECONY | Manufactured gas plant sites | Subsidiaries
Site Contingency [Line Items]
Accrued liabilities	666	676
CECONY | Other Superfund Sites | Subsidiaries
Site Contingency [Line Items]
Accrued liabilities	104	104
CECONY | Superfund Sites | Subsidiaries
Site Contingency [Line Items]
Accrued liabilities	770	780
Regulatory assets	$ 783	$ 791