Environmental Matters - Accrued Liabilities and Regulatory Assets (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Site Contingency [Line Items]
Accrued liabilities	$ 767	$ 779
Regulatory assets	4,242	4,370
Manufactured gas plant sites
Site Contingency [Line Items]
Accrued liabilities	679	689
Other Superfund Sites
Site Contingency [Line Items]
Accrued liabilities	88	90
Superfund Sites
Site Contingency [Line Items]
Accrued liabilities	767	779
Regulatory assets	774	810
CECONY
Site Contingency [Line Items]
Accrued liabilities	684	693
Regulatory assets	3,900	3,987
CECONY | Manufactured gas plant sites
Site Contingency [Line Items]
Accrued liabilities	596	603
CECONY | Other Superfund Sites
Site Contingency [Line Items]
Accrued liabilities	88	90
CECONY | Superfund Sites
Site Contingency [Line Items]
Accrued liabilities	684	693
Regulatory assets	$ 685	$ 716