Not financial advice: It depends how you earned the $1,000,000. If you won it in a lottery, had no other income, were single and only took the standard deduction, then you would owe taxes of $323,355 based on the 2012 marginal tax rates ranging from 10-35%, the 2012 standard deduction of $5,950, and the 2012 exemption amount of $3,800. This would leave you with $676,645. You may also be subject to state tax, but the exact amount varies by state.
If the $1,000,000 was a salary, your paycheck would have withholdings of $326,008 for federal taxes, Social Security tax of $4,624 and Medicare tax of $14,500, for a net paycheck (excluding any state specific withholdings and taxes and other employer deductions) of $654,868.
If the $1,000,000 was a long term capital gain, the tax would be either $0 or $150,000, depending on your ordinary income tax rate.
If the $1,000,000 were a short-term capital gain, the tax would be between $100,0000 and $350,0000, depending on your ordinary income tax rate.