The FDIC insures balances up to $250,000 per bank per tax ID. If you have a $1,000,000 and deposit $250,000 into 4 banks, the entire balance will be FDIC insured.
The above diagram is for illustration purposes.
For most companies, spreading large balances is logistically challenging and impractical (e.g., it's not realistic to open and manage accounts at 100 different banks to insure a $25 million balance).