Fair Value Measurements - Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Con Edison [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	$ 336	$ 279
Total liabilities	17	78
CECONY [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	262	227
Total liabilities	14	39
Commodity [Member] | Con Edison [Member] | Derivatives Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	82	66
Commodity [Member] | Con Edison [Member] | Derivatives Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities	15	72
Commodity [Member] | CECONY [Member] | Derivatives Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	25	30
Commodity [Member] | CECONY [Member] | Derivatives Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities	14	39
Other Assets [Member] | Con Edison [Member] | Derivatives Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	254	213
Other Assets [Member] | CECONY [Member] | Derivatives Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	237	197
Interest Rate Contract [Member] | Con Edison [Member] | Derivatives Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities	2	6
Interest Rate Contract [Member] | CECONY [Member] | Derivatives Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities
Level 1 [Member] | Con Edison [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	144	106
Total liabilities	5	12
Level 1 [Member] | CECONY [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	137	99
Total liabilities	5	12
Level 1 [Member] | Commodity [Member] | Con Edison [Member] | Derivatives Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	3
Level 1 [Member] | Commodity [Member] | Con Edison [Member] | Derivatives Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities	5	12
Level 1 [Member] | Commodity [Member] | CECONY [Member] | Derivatives Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	3
Level 1 [Member] | Commodity [Member] | CECONY [Member] | Derivatives Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities	5	12
Level 1 [Member] | Other Assets [Member] | Con Edison [Member] | Derivatives Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	141	106
Level 1 [Member] | Other Assets [Member] | CECONY [Member] | Derivatives Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	134	99
Level 1 [Member] | Interest Rate Contract [Member] | Con Edison [Member] | Derivatives Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities
Level 1 [Member] | Interest Rate Contract [Member] | CECONY [Member] | Derivatives Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities
Level 2 [Member] | Con Edison [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	243	150
Total liabilities	86	122
Level 2 [Member] | CECONY [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	116	106
Total liabilities	27	62
Level 2 [Member] | Commodity [Member] | Con Edison [Member] | Derivatives Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	130	43
Level 2 [Member] | Commodity [Member] | Con Edison [Member] | Derivatives Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities	84	116
Level 2 [Member] | Commodity [Member] | CECONY [Member] | Derivatives Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	13	8
Level 2 [Member] | Commodity [Member] | CECONY [Member] | Derivatives Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities	27	62
Level 2 [Member] | Other Assets [Member] | Con Edison [Member] | Derivatives Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	113	107
Level 2 [Member] | Other Assets [Member] | CECONY [Member] | Derivatives Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	103	98
Level 2 [Member] | Interest Rate Contract [Member] | Con Edison [Member] | Derivatives Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities	2	6
Level 2 [Member] | Interest Rate Contract [Member] | CECONY [Member] | Derivatives Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities
Level 3 [Member] | Con Edison [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	11	33
Total liabilities	2	38
Level 3 [Member] | CECONY [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	6	10
Total liabilities
Level 3 [Member] | Commodity [Member] | Con Edison [Member] | Derivatives Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	11	33
Level 3 [Member] | Commodity [Member] | Con Edison [Member] | Derivatives Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities	2	38
Level 3 [Member] | Commodity [Member] | CECONY [Member] | Derivatives Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	6	10
Level 3 [Member] | Commodity [Member] | CECONY [Member] | Derivatives Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities
Level 3 [Member] | Other Assets [Member] | Con Edison [Member] | Derivatives Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets
Level 3 [Member] | Other Assets [Member] | CECONY [Member] | Derivatives Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets
Level 3 [Member] | Interest Rate Contract [Member] | Con Edison [Member] | Derivatives Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities
Level 3 [Member] | Interest Rate Contract [Member] | CECONY [Member] | Derivatives Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities
Netting Adjustments [Member] | Con Edison [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	(62)	(10)
Total liabilities	(76)	(94)
Netting Adjustments [Member] | CECONY [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	3	12
Total liabilities	(18)	(35)
Netting Adjustments [Member] | Commodity [Member] | Con Edison [Member] | Derivatives Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	(62)	(10)
Netting Adjustments [Member] | Commodity [Member] | Con Edison [Member] | Derivatives Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities	(76)	(94)
Netting Adjustments [Member] | Commodity [Member] | CECONY [Member] | Derivatives Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	3	12
Netting Adjustments [Member] | Commodity [Member] | CECONY [Member] | Derivatives Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities	(18)	(35)
Netting Adjustments [Member] | Other Assets [Member] | Con Edison [Member] | Derivatives Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets
Netting Adjustments [Member] | Other Assets [Member] | CECONY [Member] | Derivatives Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets
Netting Adjustments [Member] | Interest Rate Contract [Member] | Con Edison [Member] | Derivatives Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities
Netting Adjustments [Member] | Interest Rate Contract [Member] | CECONY [Member] | Derivatives Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities