The rate of Hawking radiation emission (same as ideal black body radiation) is thought to be inversely proportionate to mass according to:
Therefore a million solar mass black hole would be observed at a temperature of about 0.00000000000006 deg K, and would be gaining net mass from both cosmic background radiation at 2.7 K, plus any starshine or other infalling mass source.
In the extremely distant future, if the expanding universe theory is correct, the cosmic background radiation might go low enough to cause a net mass loss...but we're talking trillions of years plus. Even then the rate of evaporation would be very slow.
Bear in mind that the radius of that million solar mass black hole's event horizon is about three million kilometers, so there's not really that much surface area to radiate from - that's only about four times larger than the Sun.