As long as you've legally gotten the million dollars you can keep the million dollars in the bank.
You can keep any amount of legally obtained money in the bank as you want too.
But if a bank fails then the FDIC only insures up to $250,000.00 per depositor in each bank.
So if you have a million dollars you should spread the million dollars across different banks and the IRS will certainly know about because the banks report any deposits or money in bank accounts that $10,000.00 or more.