To simplify the expression, we can follow the order of operations (PEMDAS/BODMAS):

First, let's simplify the exponents:
5^6 = 5 * 5 * 5 * 5 * 5 * 5 = 15625
5^3 = 5 * 5 * 5 = 125
2^3 = 2 * 2 * 2 = 8
2^2 = 2 * 2 = 4

Now, let's substitute these values back into the expression:
15625 : 125 + 8 . 4 -|-127|-18 . 5

Next, let's simplify the absolute value:
|-127| = 127

Now, let's substitute this value back into the expression:
15625 : 125 + 8 . 4 -|127|-18 . 5

Now, let's simplify the multiplication and division:
8 . 4 = 32
127 - 18 = 109

Now, let's substitute these values back into the expression:
15625 : 125 + 32 - 109 . 5

Next, let's simplify the multiplication and division:
109 . 5 = 545

Now, let's substitute this value back into the expression:
15625 : 125 + 32 - 545

Now, let's simplify the addition and subtraction:
125 + 32 = 157

Now, let's substitute this value back into the expression:
15625 : 157 - 545

Finally, let's simplify the division:
15625 : 157 ≈ 99.430

Therefore, the simplified expression is approximately 99.430.