Derivative Instruments and Hedging Activities - Realized and Unrealized Gains (Losses) on Commodity Derivatives (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Pre-tax gains/(losses) deferred in accordance with accounting rules for regulated operations:
Total deferred gains/(losses)	$ 43	$ 15	$ 38	$ (5)
Total deferred gains/(losses)	(47)	(11)	(224)	(208)
Net deferred gains/(losses)	(4)	4	(186)	(213)
Pre-tax gains/(losses) recognized in income
Total pre-tax gains/(losses) recognized in income	5	(21)	(87)	(42)
Gas purchased for resale
Pre-tax gains/(losses) recognized in income
Total pre-tax gains/(losses) recognized in income	0	1	(3)	(2)
Non-utility revenue
Pre-tax gains/(losses) recognized in income
Total pre-tax gains/(losses) recognized in income	(2)	5	3	20
Other operations and maintenance expense
Pre-tax gains/(losses) recognized in income
Total pre-tax gains/(losses) recognized in income	0	(1)	(5)	0
Other interest expense
Pre-tax gains/(losses) recognized in income
Total pre-tax gains/(losses) recognized in income	7	(26)	(82)	(60)
Deferred Derivative Gains, Current
Pre-tax gains/(losses) deferred in accordance with accounting rules for regulated operations:
Total deferred gains/(losses)	26	15	23	3
Deferred Derivative Gains, Noncurrent
Pre-tax gains/(losses) deferred in accordance with accounting rules for regulated operations:
Total deferred gains/(losses)	17	0	15	(8)
Deferred Derivative Losses, Current
Pre-tax gains/(losses) deferred in accordance with accounting rules for regulated operations:
Total deferred gains/(losses)	(9)	6	12	(32)
Recoverable Energy Costs, Current
Pre-tax gains/(losses) deferred in accordance with accounting rules for regulated operations:
Total deferred gains/(losses)	(23)	(35)	(163)	(94)
Deferred Derivative Losses, Noncurrent
Pre-tax gains/(losses) deferred in accordance with accounting rules for regulated operations:
Total deferred gains/(losses)	(15)	18	(73)	(82)
CECONY
Pre-tax gains/(losses) deferred in accordance with accounting rules for regulated operations:
Total deferred gains/(losses)	40	15	34	(2)
Total deferred gains/(losses)	(42)	(10)	(205)	(189)
Net deferred gains/(losses)	(2)	5	(171)	(191)
Pre-tax gains/(losses) recognized in income
Total pre-tax gains/(losses) recognized in income	0	(1)	(5)	0
CECONY | Gas purchased for resale
Pre-tax gains/(losses) recognized in income
Total pre-tax gains/(losses) recognized in income	0	0	0	0
CECONY | Non-utility revenue
Pre-tax gains/(losses) recognized in income
Total pre-tax gains/(losses) recognized in income	0	0	0	0
CECONY | Other operations and maintenance expense
Pre-tax gains/(losses) recognized in income
Total pre-tax gains/(losses) recognized in income	0	(1)	(5)	0
CECONY | Other interest expense
Pre-tax gains/(losses) recognized in income
Total pre-tax gains/(losses) recognized in income	0	0	0	0
CECONY | Deferred Derivative Gains, Current
Pre-tax gains/(losses) deferred in accordance with accounting rules for regulated operations:
Total deferred gains/(losses)	24	15	20	3
CECONY | Deferred Derivative Gains, Noncurrent
Pre-tax gains/(losses) deferred in accordance with accounting rules for regulated operations:
Total deferred gains/(losses)	16	0	14	(5)
CECONY | Deferred Derivative Losses, Current
Pre-tax gains/(losses) deferred in accordance with accounting rules for regulated operations:
Total deferred gains/(losses)	(11)	6	9	(28)
CECONY | Recoverable Energy Costs, Current
Pre-tax gains/(losses) deferred in accordance with accounting rules for regulated operations:
Total deferred gains/(losses)	(19)	(32)	(144)	(82)
CECONY | Deferred Derivative Losses, Noncurrent
Pre-tax gains/(losses) deferred in accordance with accounting rules for regulated operations:
Total deferred gains/(losses)	$ (12)	$ 16	$ (70)	$ (79)