The whole units of the amount. For example if currencyCode is "USD", then 1 unit is one US dollar.
Number of nano (10^-9) units of the amount. The value must be between -999,999,999 and +999,999,999 inclusive. If units is positive, nanos must be positive or zero. If units is zero, nanos can be positive, zero, or negative. If units is negative, nanos must be negative or zero. For example $-1.75 is represented as units=-1 and nanos=-750,000,000.