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041212 - Disclosure - Pension And Postretirement Benefits (Fair Value Assets Measured On Recurring Basis Unobservable Input (Level 3) Reconciliation) (Details)
(http://att.com/role/DisclosurePensionAndPostretirementBenefitsFairValueAssetsMeasuredOnRecurringBasisUnobservableInputLevel3ReconciliationDetails)
TableSchedule of Defined Benefit Plans Disclosures [Table]
Slicers (applies to each fact value in each table cell)
Reporting Entity [Axis]0000732717 (http://www.sec.gov/CIK)
Defined Benefit Plan Disclosure [Line Items]Period [Axis]
2016-01-01 - 2016-12-31
2015-01-01 - 2015-12-31
Retirement Plan Type [Axis]Retirement Plan Type [Axis]
Pension Assets [Member]Postretirement Assets [Member]Pension Assets [Member]Postretirement Assets [Member]
Defined Benefit Plan by Plan Asset Categories [Axis]Defined Benefit Plan by Plan Asset Categories [Axis]Defined Benefit Plan by Plan Asset Categories [Axis]Defined Benefit Plan by Plan Asset Categories [Axis]
Equities [Member]Fixed Income Funds [Member]Real Estate And Real Assets [Member]Plan Asset Categories [Domain]Fixed Income Funds [Member]Plan Asset Categories [Domain]Equities [Member]Fixed Income Funds [Member]Real Estate And Real Assets [Member]Plan Asset Categories [Domain]Fixed Income Funds [Member]Plan Asset Categories [Domain]
Balance, beginning of year
0  
44,000,000  
2,062,000,000  
2,106,000,000  
15,000,000  
15,000,000  
0  
51,000,000  
2,140,000,000  
2,191,000,000  
2,000,000  
2,000,000  
Realized gains (losses)
0  
(17,000,000) 
(103,000,000) 
(120,000,000) 
(2,000,000) 
(2,000,000) 
(1,000,000) 
(19,000,000) 
247,000,000  
227,000,000  
  
Unrealized gains (losses)
3,000,000  
19,000,000  
377,000,000  
399,000,000  
2,000,000  
2,000,000  
1,000,000  
16,000,000  
192,000,000  
209,000,000  
  
Transfers in
(4,000,000) 
0  
77,000,000  
73,000,000  
16,000,000  
16,000,000  
    
15,000,000  
15,000,000  
Transfers out
0  
(2,000,000) 
0  
(2,000,000) 
      
(1,000,000) 
(1,000,000) 
Purchases
3,000,000  
0  
65,000,000  
68,000,000  
  
0  
1,000,000  
195,000,000  
196,000,000  
  
Issuances
            
Sales
(1,000,000) 
(4,000,000) 
(205,000,000) 
(210,000,000) 
(5,000,000) 
(5,000,000) 
0  
(5,000,000) 
(712,000,000) 
(717,000,000) 
(1,000,000) 
(1,000,000) 
Defined Benefit Plan, Settlements, Plan Assets
            
Purchases, sales, issuances and settlements (net)
            
Balance, end of year
1,000,000  
 
40,000,000  
 
2,273,000,000  
 
2,314,000,000  
 
26,000,000  
 
26,000,000  
 
0  
 
44,000,000  
 
2,062,000,000  
 
2,106,000,000  
 
15,000,000  
 
15,000,000