Capitalization - Carrying Amounts and Fair Values of Long-Term Debt (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Unamortized debt expense	$ 142	$ 134
Carrying Amount
Debt Instrument [Line Items]
Long-Term Debt (including current portion)	16,029	14,774
Fair Value
Debt Instrument [Line Items]
Long-Term Debt (including current portion)	18,147	16,093
CECONY
Debt Instrument [Line Items]
Unamortized debt discount	121	113
CECONY \| Carrying Amount
Debt Instrument [Line Items]
Long-Term Debt (including current portion)	13,265	12,073
CECONY \| Fair Value
Debt Instrument [Line Items]
Long-Term Debt (including current portion)	$ 15,163	$ 13,268

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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- Definition

Amount of unamortized debt discount (premium) and debt issuance costs.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28555-108399

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- Definition

The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

+ References

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- Definition

The remaining balance of debt issuance expenses that were capitalized and are being amortized against income over the lives of the respective bond issues. This does not include the amounts capitalized as part of the cost of the utility plant or asset.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.17)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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