Derivative Instruments and Hedging Activities - Changes in Fair Values of Commodity Derivatives (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Pre-tax gains/(losses) deferred in accordance with accounting rules for regulated operations:
Total deferred gains/(losses)	$ 14	$ (1)
Total deferred gains/(losses)	35	(108)
Net deferred gains/(losses)	49	(109)
Pre-tax gain/(loss) recognized in income
Total pre-tax gain/(loss) recognized in income	72	(70)
Deferred Derivative Gains, Current [Member]
Pre-tax gains/(losses) deferred in accordance with accounting rules for regulated operations:
Total deferred gains/(losses)	14	(1)
Regulatory Liabilities, Long-term [Member]
Pre-tax gains/(losses) deferred in accordance with accounting rules for regulated operations:
Total deferred gains/(losses)
Deferred Derivative Losses, Current [Member]
Pre-tax gains/(losses) deferred in accordance with accounting rules for regulated operations:
Total deferred gains/(losses)	47	95
Recoverable Energy Costs, Current [Member]
Pre-tax gains/(losses) deferred in accordance with accounting rules for regulated operations:
Total deferred gains/(losses)	(39)	(220)
Long-term [Member]
Pre-tax gains/(losses) deferred in accordance with accounting rules for regulated operations:
Total deferred gains/(losses)	27	17
CECONY [Member]
Pre-tax gains/(losses) deferred in accordance with accounting rules for regulated operations:
Total deferred gains/(losses)	11	(1)
Total deferred gains/(losses)	14	(88)
Net deferred gains/(losses)	25	(89)
Pre-tax gain/(loss) recognized in income
Total pre-tax gain/(loss) recognized in income
CECONY [Member] | Deferred Derivative Gains, Current [Member]
Pre-tax gains/(losses) deferred in accordance with accounting rules for regulated operations:
Total deferred gains/(losses)	11	(1)
CECONY [Member] | Regulatory Liabilities, Long-term [Member]
Pre-tax gains/(losses) deferred in accordance with accounting rules for regulated operations:
Total deferred gains/(losses)
CECONY [Member] | Deferred Derivative Losses, Current [Member]
Pre-tax gains/(losses) deferred in accordance with accounting rules for regulated operations:
Total deferred gains/(losses)	38	80
CECONY [Member] | Recoverable Energy Costs, Current [Member]
Pre-tax gains/(losses) deferred in accordance with accounting rules for regulated operations:
Total deferred gains/(losses)	(37)	(192)
CECONY [Member] | Long-term [Member]
Pre-tax gains/(losses) deferred in accordance with accounting rules for regulated operations:
Total deferred gains/(losses)	13	24
Purchased Power Expense [Member]
Pre-tax gain/(loss) recognized in income
Total pre-tax gain/(loss) recognized in income	90	(54)
Purchased Power Expense [Member] | CECONY [Member]
Pre-tax gain/(loss) recognized in income
Total pre-tax gain/(loss) recognized in income
Gas Purchased for Resale [Member]
Pre-tax gain/(loss) recognized in income
Total pre-tax gain/(loss) recognized in income	(27)	(5)
Gas Purchased for Resale [Member] | CECONY [Member]
Pre-tax gain/(loss) recognized in income
Total pre-tax gain/(loss) recognized in income
Non-utility Revenue [Member]
Pre-tax gain/(loss) recognized in income
Total pre-tax gain/(loss) recognized in income	9	(11)
Non-utility Revenue [Member] | CECONY [Member]
Pre-tax gain/(loss) recognized in income
Total pre-tax gain/(loss) recognized in income