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Employee Benefits - Additional Information (Detail) - MXN ($)
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Disclosure of defined benefit plans [line items]        
Current service cost $ 2,810,584,000 $ 2,591,975,000 $ 3,322,813,000  
Expected return on plan assets (17,655,119,000) 20,070,037,000 20,804,104,000  
Net pension plan liability and plan assets $ (154,847,297,000) (140,696,974,000) (108,118,868,000) $ (107,944,581,000)
Severance benefit obligations, description Severance benefit obligations for employees hired before January 1, 2003, excluding civil servants, are covered by defined benefit plans. Upon termination by A1 Telekom Austria Group or retirement, eligible employees receive severance payments. Depending on their time in service, their severance is equal to a multiple of their monthly basic compensation plus variable elements such as overtime or bonuses, with a maximum of twelve monthly salaries. In case of death, the heirs of eligible employees receive 50% of the severance benefits. The primary risks to A1 Telekom Austria Group are salary increases and changes of interest rates.      
Severance benefits, in case of death 50.00%      
Net period cost (benefit) $ 18,085,954,000 $ 16,609,565,000 $ 13,989,100,000  
Akenes [member]        
Disclosure of defined benefit plans [line items]        
Defined Benefit Plan, Pension Benefit Obligation, Percentage 10.00% 10.00%    
Telekom Austria [member]        
Disclosure of defined benefit plans [line items]        
Defined benefits plan, eligibility retirement date Jan. 01, 1975      
Telekom Austria [member] | Defined Contribution Plans [member]        
Disclosure of defined benefit plans [line items]        
Annual expense of defined contribution plan $ 295,567,000 $ 281,693    
Telekom Austria [member] | Unfunded Pension Plans [member]        
Disclosure of defined benefit plans [line items]        
Benefit determination maximum percentage on salary before retirement 80.00%      
Telmexs [member]        
Disclosure of defined benefit plans [line items]        
Net pension plan liability and plan assets $ 150,090,481,000 $ 164,910,346,000    
Rate of equity instruments   31.90%    
Rate of debt instruments 39.60%      
Recorded of pension plan re-measurement value in defined pension plan $ 11,753,416,000 $ 34,782,129,000    
Increase in fair value of related party pension plan investments $ 14,820,220,000 4,156,919,000    
Plan description Part of the Telmex's employees are covered under defined benefit pension plans and seniority premiums. Pension benefits and seniority premiums are determined on the basis of compensation received by the employees in their final year of employment, their seniority, and their age at the time of retirement. Telmex has set up an irrevocable trust fund to finance these employee benefits and has adopted the policy of making contributions to such fund when it is considered necessary.      
Top of range [member] | Telekom Austria [member] | Defined Contribution Plans [member]        
Disclosure of defined benefit plans [line items]        
Percentage of defined contribution plan 5.00%      
Austria [member]        
Disclosure of defined benefit plans [line items]        
Service award description Civil servants and certain employees (in the following “employees”) are eligible to receive service awards. In accordance with the legal regulations, eligible employees receive a cash bonus of two months’ salary after 25 years of service and four months’ salary after 40 years of service. Employees with at least 35 years of service when retiring (at the age of 65) or who are retiring based on specific legal regulations are also eligible to receive the service award of four monthly salaries. The obligation is accrued over the period of service, taking into account the employee turnover rate of employees who leave service early. The main risk that A1 Telekom Austria Group is exposed to is the risk of development of salary increases and changes of interest rates.      
Service period to receive bonus, description after 25 years      
Service period to receive bonus, description after 40 years      
Contributions to social security, net of the share contributed by civil servants $ 1,474,721,000 1,334,713,000    
Contributions to the government, net of the share contributed by civil servants 601,476,000 530,888,000    
Austria [member] | Defined Contribution Plans [member]        
Disclosure of defined benefit plans [line items]        
DCP liability 134,034,000 111,724,000    
Austria [member] | Telekom Austria [member]        
Disclosure of defined benefit plans [line items]        
Percentage of contribution to social security     12.55%  
Austria [member] | Telekom Austria [member] | Defined Contribution Plans [member]        
Disclosure of defined benefit plans [line items]        
Defined contribution plan, payment $ 66,294,000 54,945,000    
Austria [member] | Bottom of range [member]        
Disclosure of defined benefit plans [line items]        
Service period to receive bonus, description 35 years of service when retiring (at the age of 65)      
Percentage of contribution to active civil servants 7.00%      
Austria [member] | Top of range [member]        
Disclosure of defined benefit plans [line items]        
Percentage of contribution to active civil servants 29.00%      
Brazil [member]        
Disclosure of defined benefit plans [line items]        
Current service cost $ 268,562,000 99,498,000 $ 98,658,000  
Employee benefits 2,111,801,000 2,402,285,000    
Cost of labor 2,930,000 3,365,000 2,377,000  
Net period cost (benefit) 722,412,000 511,964,000 579,432,000  
Employee benefits 2,111,801,000 2,402,285,000    
Brazil [member] | Claro Brasil [member] | Defined Contribution Plans [member]        
Disclosure of defined benefit plans [line items]        
DCP liability $ 980,014,000 76,509,000    
Brazil [member] | Bottom of range [member] | Claro Brasil [member] | Participants enrolled before October 31st, 2014 [member]        
Disclosure of defined benefit plans [line items]        
Employee contributions to the plan 1.00%      
Brazil [member] | Bottom of range [member] | Claro Brasil [member] | Participants enrolled after October 31st, 2014 [member]        
Disclosure of defined benefit plans [line items]        
Employee contributions to the plan 1.00%      
Brazil [member] | Top of range [member] | Claro Brasil [member]        
Disclosure of defined benefit plans [line items]        
Employer contributions to the plan 8.00%      
Brazil [member] | Top of range [member] | Claro Brasil [member] | Participants enrolled before October 31st, 2014 [member]        
Disclosure of defined benefit plans [line items]        
Employee contributions to the plan 8.00%      
Brazil [member] | Top of range [member] | Claro Brasil [member] | Participants enrolled after October 31st, 2014 [member]        
Disclosure of defined benefit plans [line items]        
Employee contributions to the plan 7.00%      
Mexico [member]        
Disclosure of defined benefit plans [line items]        
Current service cost   49,050,000 16,347,000  
Expected return on plan assets $ 174,994,000      
Employee benefits 916,534,000 845,830,000    
Net period cost (benefit) 14,911,208,000 12,788,464,000 12,046,208,000  
Ecuador [member]        
Disclosure of defined benefit plans [line items]        
Current service cost 67,402,000 34,425,000 58,354,000  
Employee benefits 488,161,000 409,750,000    
Net period cost (benefit) 67,402,000 34,425,000 $ 58,354,000  
Employee benefits 488,161,000 $ 409,750,000    
Central America [Member]        
Disclosure of defined benefit plans [line items]        
Employee benefits 250,819,000      
Net period cost (benefit) 19,462,000      
Employee benefits $ 250,819,000