James has it correctly. What's with all the opinions "This is the only way" errors prior to his statement? Yes, 1 million is 1M, 1 thousand is 1k (note the small 'k'), one thousandth is 1m (milli), and one millionth is 1u (micro). NEVER use MM. 1 billion is 1G (Giga = 10^9), and for your rich dreamers, 1 trillion is 1T (Tera).
From high-to-low: 1E12 (1 followed by 12 zeros) = 1T (tera), 1E9 = 1G (giga), 1E6 = 1M (mega), 1E3= 1k (kilo), 1E-2= 0.01= 1d (deci), 1E-3= 1m (milli), 1E-6 = 1u (micro), 1E-9=1n (nano), and 1E-12 = 1p (pico).
Note which are small vs capitalized