Debt (Revolving Credit Agreement) (Narrative) (Details) - Revolving Credit Facility [Member] - USD ($) $ in Millions	1 Months Ended	12 Months Ended
Dec. 31, 2015	Dec. 31, 2017
Debt Instrument [Line Items]
Face amount or capacity of debt (in millions)	$ 12,000
Credit agreement - initiation date	Dec. 31, 2015
Term of Loan	5 years
Credit agreement - advances outstanding		$ 0
Ratio of net debt to EBITDA covenant		3.5 to 1
Credit agreement - maturity date		Dec. 11, 2020
Credit agreement - maximum potential extension of term (years)		2 years
Credit agreement - minimum borrowing capacity		$ 0
Credit agreement - minimum lender approval percentage for extension of term (in hundredths)		50.00%
Credit agreement - base rate		• at a variable annual rate equal to (1) the highest of: (a) the base rate of the bank affiliate of Citibank, N.A., (b) 0.50% per annum above the federal funds rate, and (c) the London Interbank Offered Rate (LIBOR) applicable to U.S. dollars for a period of one month plus 1.00% per annum, plus (2) an applicable margin (as set forth in this agreement); or • at a rate equal to: (i) LIBOR for a period of one, two, three or six months, as applicable, plus (ii) an applicable margin (as set forth in this agreement).
Additional Margin Upon Default [Member] \| High Credit Rating [Member]
Debt Instrument [Line Items]
Credit agreement - basis spread of variable rate		2.00%
Additional Margin Upon Default [Member] \| Moderate Credit Rating [Member]
Debt Instrument [Line Items]
Credit agreement - basis spread of variable rate		2.00%
Additional Margin Upon Default [Member] \| Low Credit Rating [Member]
Debt Instrument [Line Items]
Credit agreement - basis spread of variable rate		2.00%
Additional Margin Upon Default [Member] \| Very Low Credit Rating [Member]
Debt Instrument [Line Items]
Credit agreement - basis spread of variable rate		2.00%
Facility Fee [Member] \| High Credit Rating [Member]
Debt Instrument [Line Items]
Credit agreement - commitment fee percentage		0.07%
Facility Fee [Member] \| Moderate Credit Rating [Member]
Debt Instrument [Line Items]
Credit agreement - commitment fee percentage		0.09%
Facility Fee [Member] \| Low Credit Rating [Member]
Debt Instrument [Line Items]
Credit agreement - commitment fee percentage		0.10%
Facility Fee [Member] \| Very Low Credit Rating [Member]
Debt Instrument [Line Items]
Credit agreement - commitment fee percentage		0.125%

Line Of Credit Facility Covenant Debt Ratio

No definition available.

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Namespace Prefix:	t_
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Balance Type:	na
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- Definition

Minimum amount of borrowing capacity at the discretion of the company as debtor.

+ References

No definition available.

+ Details

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Balance Type:	credit
Period Type:	instant

- Definition

Minimum lender approval level for an extension of the term of a credit agreement.

+ References

No definition available.

+ Details

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- Definition

Potential extension of term of short-term credit agreement (in years).

+ References

No definition available.

+ Details

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- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

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Period Type:	duration

- Definition

The reference rate for the variable rate of the debt instrument, such as LIBOR or the US Treasury rate and the maturity of the reference rate used, such as three months or six months LIBOR.

+ References

No definition available.

+ Details

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- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=64930739&loc=d3e28878-108400

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28551-108399

+ Details

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Period Type:	instant

- Definition

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.

+ References

No definition available.

+ Details

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- Definition

Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

+ References

+ Details

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- Definition

Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

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- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ 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(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

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Balance Type:	credit
Period Type:	instant

- Definition

The fee, expressed as a percentage of the line of credit facility, for the line of credit facility regardless of whether the facility has been used.

+ References

No definition available.

+ Details

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- Definition

Date the credit facility first became available, in CCYY-MM-DD format.

+ References

+ Details

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- Details

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- Details

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- Details

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