Derivative Instruments and Hedging Activities - Realized and Unrealized Gains (Losses) on Commodity Derivatives (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Pre-tax gains/(losses) deferred in accordance with accounting rules for regulated operations:
Total deferred gains/(losses)	$ (8)	$ (18)	$ (6)	$ (20)
Total deferred gains/(losses)	(22)	(151)	(176)	(198)
Net deferred gains/(losses)	(30)	(169)	(182)	(218)
Pre-tax gains/(losses) recognized in income
Total pre-tax gains/(losses) recognized in income	(1)	(17)	(92)	(20)
Gas purchased for resale
Pre-tax gains/(losses) recognized in income
Total pre-tax gains/(losses) recognized in income			(3)	(2)
Non-utility revenue
Pre-tax gains/(losses) recognized in income
Total pre-tax gains/(losses) recognized in income	1	7	5	15
Other operations and maintenance expense
Pre-tax gains/(losses) recognized in income
Total pre-tax gains/(losses) recognized in income	2	0	(5)	1
Other interest expense
Pre-tax gains/(losses) recognized in income
Total pre-tax gains/(losses) recognized in income	(4)	(24)	(89)	(34)
Deferred Derivative Gains, Current
Pre-tax gains/(losses) deferred in accordance with accounting rules for regulated operations:
Total deferred gains/(losses)	(2)	(16)	(3)	(12)
Deferred Derivative Gains, Noncurrent
Pre-tax gains/(losses) deferred in accordance with accounting rules for regulated operations:
Total deferred gains/(losses)	(6)	(2)	(3)	(8)
Deferred Derivative Losses, Current
Pre-tax gains/(losses) deferred in accordance with accounting rules for regulated operations:
Total deferred gains/(losses)	36	(36)	22	(39)
Recoverable Energy Costs, Current
Pre-tax gains/(losses) deferred in accordance with accounting rules for regulated operations:
Total deferred gains/(losses)	(45)	(41)	(140)	(59)
Deferred Derivative Losses, Noncurrent
Pre-tax gains/(losses) deferred in accordance with accounting rules for regulated operations:
Total deferred gains/(losses)	(13)	(74)	(58)	(100)
CECONY
Pre-tax gains/(losses) deferred in accordance with accounting rules for regulated operations:
Total deferred gains/(losses)	(8)	(15)	(6)	(17)
Total deferred gains/(losses)	(23)	(139)	(164)	(180)
Net deferred gains/(losses)	(31)	(154)	(170)	(197)
Pre-tax gains/(losses) recognized in income
Total pre-tax gains/(losses) recognized in income	2	0	(5)	1
CECONY | Gas purchased for resale
Pre-tax gains/(losses) recognized in income
Total pre-tax gains/(losses) recognized in income			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	2	0	(5)	1
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)	(2)	(15)	(3)	(11)
CECONY | Deferred Derivative Gains, Noncurrent
Pre-tax gains/(losses) deferred in accordance with accounting rules for regulated operations:
Total deferred gains/(losses)	(6)	0	(3)	(6)
CECONY | Deferred Derivative Losses, Current
Pre-tax gains/(losses) deferred in accordance with accounting rules for regulated operations:
Total deferred gains/(losses)	32	(34)	20	(34)
CECONY | Recoverable Energy Costs, Current
Pre-tax gains/(losses) deferred in accordance with accounting rules for regulated operations:
Total deferred gains/(losses)	(40)	(37)	(126)	(51)
CECONY | Deferred Derivative Losses, Noncurrent
Pre-tax gains/(losses) deferred in accordance with accounting rules for regulated operations:
Total deferred gains/(losses)	$ (15)	$ (68)	$ (58)	$ (95)