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, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Pre-tax gains/(losses) deferred in accordance with accounting rules for regulated operations:
Total deferred gains/(losses)	$ 15	$ 6	$ (5)	$ (6)
Total deferred gains/(losses)	(11)	36	(208)	31
Net deferred gains/(losses)	4	42	(213)	25
Pre-tax gains/(losses) recognized in income
Total pre-tax gains/(losses) recognized in income	(21)	(7)	(42)	(8)
Gas purchased for resale
Pre-tax gains/(losses) recognized in income
Total pre-tax gains/(losses) recognized in income	1	0	(2)	(1)
Non-utility revenue
Pre-tax gains/(losses) recognized in income
Total pre-tax gains/(losses) recognized in income	5	(7)	20	(7)
Other interest expense
Pre-tax gains/(losses) recognized in income
Total pre-tax gains/(losses) recognized in income	(26)	0	(60)	0
Other operations and maintenance expense
Pre-tax gains/(losses) recognized in income
Total pre-tax gains/(losses) recognized in income	(1)	0
Deferred Derivative Gains, Current
Pre-tax gains/(losses) deferred in accordance with accounting rules for regulated operations:
Total deferred gains/(losses)	15	6	3	(11)
Deferred Derivative Gains, Noncurrent
Pre-tax gains/(losses) deferred in accordance with accounting rules for regulated operations:
Total deferred gains/(losses)	0	0	(8)	5
Deferred Derivative Losses, Current
Pre-tax gains/(losses) deferred in accordance with accounting rules for regulated operations:
Total deferred gains/(losses)	6	25	(32)	21
Recoverable Energy Costs, Current
Pre-tax gains/(losses) deferred in accordance with accounting rules for regulated operations:
Total deferred gains/(losses)	(35)	(4)	(94)	(13)
Deferred Derivative Losses, Noncurrent
Pre-tax gains/(losses) deferred in accordance with accounting rules for regulated operations:
Total deferred gains/(losses)	18	15	(82)	23
CECONY
Pre-tax gains/(losses) deferred in accordance with accounting rules for regulated operations:
Total deferred gains/(losses)	15	8	(2)	(6)
Total deferred gains/(losses)	(10)	33	(189)	30
Net deferred gains/(losses)	5	41	(191)	24
Pre-tax gains/(losses) recognized in income
Total pre-tax gains/(losses) recognized in income	(1)	0	0	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 interest expense
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	(1)
CECONY | Deferred Derivative Gains, Current
Pre-tax gains/(losses) deferred in accordance with accounting rules for regulated operations:
Total deferred gains/(losses)	15	6	3	(10)
CECONY | Deferred Derivative Gains, Noncurrent
Pre-tax gains/(losses) deferred in accordance with accounting rules for regulated operations:
Total deferred gains/(losses)	0	2	(5)	4
CECONY | Deferred Derivative Losses, Current
Pre-tax gains/(losses) deferred in accordance with accounting rules for regulated operations:
Total deferred gains/(losses)	6	25	(28)	23
CECONY | Recoverable Energy Costs, Current
Pre-tax gains/(losses) deferred in accordance with accounting rules for regulated operations:
Total deferred gains/(losses)	(32)	(6)	(82)	(14)
CECONY | Deferred Derivative Losses, Noncurrent
Pre-tax gains/(losses) deferred in accordance with accounting rules for regulated operations:
Total deferred gains/(losses)	$ 16	$ 14	$ (79)	$ 21