v3.26.1
Employee Benefit Plan, Master Trust (AT&T Master Trust Assets at Fair Value) (Details) - EBP-43-1301883-022 [Master Trust] - USD ($)
$ in Thousands
Dec. 31, 2025
Dec. 31, 2024
EBP, Investment, Fair Value and NAV [Line Items]    
Assets at fair value $ 45,305,719 $ 42,649,973
EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value 34,518,159 31,848,071
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 7,802,816 7,151,030
Fair Value, Inputs, Level 1    
EBP, Investment, Fair Value and NAV [Line Items]    
EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value 7,768,827 7,121,340
Fair Value, Inputs, Level 2    
EBP, Investment, Fair Value and NAV [Line Items]    
EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value 33,989 29,690
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
Cash and Cash Equivalents [Member]    
EBP, Investment, Fair Value and NAV [Line Items]    
EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value 42  
Cash and Cash Equivalents [Member] | 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 42  
Cash and Cash Equivalents [Member] | Fair Value, Inputs, Level 1    
EBP, Investment, Fair Value and NAV [Line Items]    
EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value 42  
Cash and Cash Equivalents [Member] | Fair Value, Inputs, Level 2    
EBP, Investment, Fair Value and NAV [Line Items]    
EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value 0  
Cash and Cash Equivalents [Member] | Fair Value, Inputs, Level 3    
EBP, Investment, Fair Value and NAV [Line Items]    
EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value 0  
AT&T common stock    
EBP, Investment, Fair Value and NAV [Line Items]    
EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value 4,023,865 3,859,277
AT&T common stock | 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 4,023,865 3,859,277
AT&T common stock | Fair Value, Inputs, Level 1    
EBP, Investment, Fair Value and NAV [Line Items]    
EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value 4,023,865 3,859,277
AT&T common stock | Fair Value, Inputs, Level 2    
EBP, Investment, Fair Value and NAV [Line Items]    
EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value 0 0
AT&T common stock | 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
Mutual funds    
EBP, Investment, Fair Value and NAV [Line Items]    
EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value 42,365 48,445
Mutual funds | 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 42,365 48,445
Mutual funds | Fair Value, Inputs, Level 1    
EBP, Investment, Fair Value and NAV [Line Items]    
EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value 42,365 48,445
Mutual funds | Fair Value, Inputs, Level 2    
EBP, Investment, Fair Value and NAV [Line Items]    
EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value 0 0
Mutual funds | 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
Self-directed brokerage accounts | 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 3,736,544 3,243,308
Self-directed brokerage accounts | Fair Value, Inputs, Level 1    
EBP, Investment, Fair Value and NAV [Line Items]    
EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value 3,702,555 3,213,618
Self-directed brokerage accounts | Fair Value, Inputs, Level 2    
EBP, Investment, Fair Value and NAV [Line Items]    
EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value 33,989 29,690
Self-directed brokerage accounts | 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
Common/collective trust funds    
EBP, Investment, Fair Value and NAV [Line Items]    
EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value 26,715,343 24,697,041
Asset Allocation Funds    
EBP, Investment, Fair Value and NAV [Line Items]    
EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value 8,356,475 7,544,658
UNITED STATES | Total U.S. Stock Market Index Fund    
EBP, Investment, Fair Value and NAV [Line Items]    
EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value 3,028,277 2,774,504
UNITED STATES | Large Cap U.S. Stock Index Fund    
EBP, Investment, Fair Value and NAV [Line Items]    
EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value 9,342,538 8,803,530
UNITED STATES | Small and Mid-Sized U.S. Stock Index Fund    
EBP, Investment, Fair Value and NAV [Line Items]    
EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value 3,043,821 3,141,256
Non-US [Member] | International Stock Index Fund    
EBP, Investment, Fair Value and NAV [Line Items]    
EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value $ 2,944,232 $ 2,433,093