"Amounts are double-precision floating point numbers."

This is incorrect. "Floating point" means a certain lossy-compression technique to generate approximations of numbers at the cost of sometimes being inaccurate. For example, if you're using floating point, 0.1 * 0.1 is not equal to 0.01. Worse, it isn't even the closest number to 0.01 that could be represented using this lossy compression format. Fortunately, we don't use floating point to represent amounts of Zcash, ever. I think what the help text means to say is that amounts are decimal numbers.