Summary of Significant Accounting Policies - Federal Income Tax (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($)
Income Taxes Disclosure [Line Items]
Decrease in net deferred tax liabilities resulting from TCJA	$ 5,312
Change in net income resulting from TCJA	259
Future Income Tax
Income Taxes Disclosure [Line Items]
Increase in regulatory liability resulting from TCJA	3,713
Future Income Tax
Income Taxes Disclosure [Line Items]
Decrease in regulatory asset resulting from TCJA	1,250
Revenue Taxes
Income Taxes Disclosure [Line Items]
Decrease in regulatory asset resulting from TCJA	90
CECONY
Income Taxes Disclosure [Line Items]
Decrease in net deferred tax liabilities resulting from TCJA	4,781
CECONY | Future Income Tax
Income Taxes Disclosure [Line Items]
Increase in regulatory liability resulting from TCJA	3,513
CECONY | Future Income Tax
Income Taxes Disclosure [Line Items]
Decrease in regulatory asset resulting from TCJA	1,182
CECONY | Revenue Taxes
Income Taxes Disclosure [Line Items]
Decrease in regulatory asset resulting from TCJA	$ 86