v3.26.1
Employee Benefit Plan, Master Trust (AT&T Group Trust Assets at Fair Value) (Details) - EBP-43-1301883-021 [Group Trust] - USD ($)
$ in Thousands
Dec. 31, 2025
Dec. 31, 2024
EBP, Investment, Fair Value and NAV [Line Items]    
EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value $ 7,170,886 $ 6,862,851
Mortgage-backed securities    
EBP, Investment, Fair Value and NAV [Line Items]    
EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value 816,124 843,105
Corporate debt    
EBP, Investment, Fair Value and NAV [Line Items]    
EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value 874,643 939,989
Equity Securities [Member]    
EBP, Investment, Fair Value and NAV [Line Items]    
EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value 989,007 589,466
Mutual Fund [Member]    
EBP, Investment, Fair Value and NAV [Line Items]    
EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value 174,429 202,817
US Treasury and Government [Member]    
EBP, Investment, Fair Value and NAV [Line Items]    
EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value 505,762 319,763
Common/collective trust funds    
EBP, Investment, Fair Value and NAV [Line Items]    
EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value 3,807,953 3,962,205
Derivative [Member]    
EBP, Investment, Fair Value and NAV [Line Items]    
EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value 23  
Fair Value, Inputs, Level 1, Level 2, and Level 3    
EBP, Investment, Fair Value and NAV [Line Items]    
EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value 3,362,933 2,900,646
Fair Value, Inputs, Level 1, Level 2, and Level 3 | Mortgage-backed securities    
EBP, Investment, Fair Value and NAV [Line Items]    
EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value 816,124 843,105
Fair Value, Inputs, Level 1, Level 2, and Level 3 | Corporate debt    
EBP, Investment, Fair Value and NAV [Line Items]    
EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value 874,643 939,989
Fair Value, Inputs, Level 1, Level 2, and Level 3 | Equity Securities [Member]    
EBP, Investment, Fair Value and NAV [Line Items]    
EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value 989,007 589,466
Fair Value, Inputs, Level 1, Level 2, and Level 3 | Mutual Fund [Member]    
EBP, Investment, Fair Value and NAV [Line Items]    
EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value 174,429 202,817
Fair Value, Inputs, Level 1, Level 2, and Level 3 | US Treasury and Government [Member]    
EBP, Investment, Fair Value and NAV [Line Items]    
EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value 505,762 319,763
Fair Value, Inputs, Level 1, Level 2, and Level 3 | Derivative [Member]    
EBP, Investment, Fair Value and NAV [Line Items]    
Liability at fair value   (2,534)
EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value 23  
Fair Value, Inputs, Level 1    
EBP, Investment, Fair Value and NAV [Line Items]    
EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value 1,166,404 797,789
Fair Value, Inputs, Level 1 | Mortgage-backed securities    
EBP, Investment, Fair Value and NAV [Line Items]    
EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value 0 0
Fair Value, Inputs, Level 1 | Corporate debt    
EBP, Investment, Fair Value and NAV [Line Items]    
EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value 0 0
Fair Value, Inputs, Level 1 | Equity Securities [Member]    
EBP, Investment, Fair Value and NAV [Line Items]    
EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value 989,007 589,466
Fair Value, Inputs, Level 1 | Mutual Fund [Member]    
EBP, Investment, Fair Value and NAV [Line Items]    
EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value 174,429 202,817
Fair Value, Inputs, Level 1 | US Treasury and Government [Member]    
EBP, Investment, Fair Value and NAV [Line Items]    
EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value 0 0
Fair Value, Inputs, Level 1 | Derivative [Member]    
EBP, Investment, Fair Value and NAV [Line Items]    
Liability at fair value   (2,534)
EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value 23  
Fair Value, Inputs, Level 2    
EBP, Investment, Fair Value and NAV [Line Items]    
EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value 2,196,529 2,102,857
Fair Value, Inputs, Level 2 | Mortgage-backed securities    
EBP, Investment, Fair Value and NAV [Line Items]    
EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value 816,124 843,105
Fair Value, Inputs, Level 2 | Corporate debt    
EBP, Investment, Fair Value and NAV [Line Items]    
EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value 874,643 939,989
Fair Value, Inputs, Level 2 | Equity Securities [Member]    
EBP, Investment, Fair Value and NAV [Line Items]    
EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value 0 0
Fair Value, Inputs, Level 2 | Mutual Fund [Member]    
EBP, Investment, Fair Value and NAV [Line Items]    
EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value 0 0
Fair Value, Inputs, Level 2 | US Treasury and Government [Member]    
EBP, Investment, Fair Value and NAV [Line Items]    
EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value 505,762 319,763
Fair Value, Inputs, Level 2 | Derivative [Member]    
EBP, Investment, Fair Value and NAV [Line Items]    
Liability at fair value   0
EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value 0  
Fair Value, Inputs, Level 3    
EBP, Investment, Fair Value and NAV [Line Items]    
EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value 0 0
Fair Value, Inputs, Level 3 | Mortgage-backed securities    
EBP, Investment, Fair Value and NAV [Line Items]    
EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value 0 0
Fair Value, Inputs, Level 3 | Corporate debt    
EBP, Investment, Fair Value and NAV [Line Items]    
EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value 0 0
Fair Value, Inputs, Level 3 | Equity Securities [Member]    
EBP, Investment, Fair Value and NAV [Line Items]    
EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value 0 0
Fair Value, Inputs, Level 3 | Mutual Fund [Member]    
EBP, Investment, Fair Value and NAV [Line Items]    
EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value 0 0
Fair Value, Inputs, Level 3 | US Treasury and Government [Member]    
EBP, Investment, Fair Value and NAV [Line Items]    
EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value 0 0
Fair Value, Inputs, Level 3 | Derivative [Member]    
EBP, Investment, Fair Value and NAV [Line Items]    
Liability at fair value   0
EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value 0  
Fair Value Measured at Net Asset Value Per Share [Member] | 103-12 investments    
EBP, Investment, Fair Value and NAV [Line Items]    
EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value 235,273 207,042
Fair Value Measured at Net Asset Value Per Share [Member] | EBP, Other Investment [Member]    
EBP, Investment, Fair Value and NAV [Line Items]    
EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value 162,302 74,483
UNITED STATES | Fair Value Measured at Net Asset Value Per Share [Member] | Common/collective trust funds    
EBP, Investment, Fair Value and NAV [Line Items]    
EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value 3,219,358 3,542,987
Non-US [Member] | Cash and Cash Equivalents [Member]    
EBP, Investment, Fair Value and NAV [Line Items]    
EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value 2,945 8,040
Non-US [Member] | Fair Value, Inputs, Level 1, Level 2, and Level 3 | Cash and Cash Equivalents [Member]    
EBP, Investment, Fair Value and NAV [Line Items]    
EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value 2,945 8,040
Non-US [Member] | Fair Value, Inputs, Level 1 | Cash and Cash Equivalents [Member]    
EBP, Investment, Fair Value and NAV [Line Items]    
EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value 2,945 8,040
Non-US [Member] | Fair Value, Inputs, Level 2 | Cash and Cash Equivalents [Member]    
EBP, Investment, Fair Value and NAV [Line Items]    
EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value 0 0
Non-US [Member] | Fair Value, Inputs, Level 3 | Cash and Cash Equivalents [Member]    
EBP, Investment, Fair Value and NAV [Line Items]    
EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value 0 0
Non-US [Member] | Fair Value Measured at Net Asset Value Per Share [Member] | Common/collective trust funds    
EBP, Investment, Fair Value and NAV [Line Items]    
EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value $ 191,020 $ 137,693