v3.26.1
Average Annual Total Returns - American Century Mutual Funds, Inc
 12 Months Ended 60 Months Ended 120 Months Ended
Mar. 01, 2026
Dec. 31, 2025
Dec. 31, 2025
Dec. 31, 2025
S&P 500® Index        
Prospectus [Line Items]        
Average Annual Return, Label [Optional Text] S&P 500® Index   (reflects no deduction for fees, expenses or taxes)      
Average Annual Return, Percent   17.88% 14.42% 14.82%
Bloomberg US Aggregate Bond Index        
Prospectus [Line Items]        
Average Annual Return, Label [Optional Text] Bloomberg U.S. Aggregate Bond Index   (reflects no deduction for fees, expenses or taxes)      
Average Annual Return, Percent   7.30% (0.36%) 2.01%
Blended Index        
Prospectus [Line Items]        
Average Annual Return, Label [Optional Text] Blended Index   (reflects no deduction for fees, expenses or taxes)      
Average Annual Return, Percent   13.70% 8.47% 9.78%
BALANCED FUND, INVESTOR CLASS        
Prospectus [Line Items]        
Average Annual Return, Label [Optional Text] Investor Class Return Before Taxes      
Average Annual Return, Percent   9.60% 6.45% 7.99%
BALANCED FUND, INVESTOR CLASS | After Taxes on Distributions        
Prospectus [Line Items]        
Average Annual Return, Label [Optional Text] Return After Taxes on Distributions      
Average Annual Return, Percent   8.93% 4.77% 6.38%
BALANCED FUND, INVESTOR CLASS | After Taxes on Distributions and Sales        
Prospectus [Line Items]        
Average Annual Return, Label [Optional Text] Return After Taxes on Distributions and Sale of Fund Shares      
Average Annual Return, Percent   5.78% 4.48% 5.91%
BALANCED FUND, I CLASS        
Prospectus [Line Items]        
Average Annual Return, Label [Optional Text] I Class Return Before Taxes      
Average Annual Return, Percent   9.75% 6.66% 8.21%
BALANCED FUND, R5 CLASS        
Prospectus [Line Items]        
Average Annual Return, Label [Optional Text] [1] R5 Class1 Return Before Taxes      
Average Annual Return, Percent [1]   9.81% 6.66% 8.21%
[1] Historical performance for the R5 Class prior to its inception (April 10, 2017) is based on the performance of I Class shares, which have the same expenses as the R5 Class.