What does the "value" field of the tangle explorer indicates? The linked transaction reports a value of 1+ B USD. What is this value referring to?
When you check the associated bundle, you will see that the bundle transfers the money from address
ZJBSFPLRDZUUJKYMRQ9OYQ9NZTGYYWAYEVLYOUY9XQHWFESPRFDKJSEJKUSRLSXIZNGIZZBTWLZWIQXJD to the same address
ZJBSFPLRDZUUJKYMRQ9OYQ9NZTGYYWAYEVLYOUY9XQHWFESPRFDKJSEJKUSRLSXIZNGIZZBTWLZWIQXJD. In other words, this transaction is equivalent to sending money to your own bank account (the same one you are sending from).
The IOTA protocol will only ensure that the amount that is sent is equal to the amount received, and that there are no negative balances at the end of the transaction.
Therefore, you can do such a transaction with any value (up to the maximum supply of 2,779,530,283,277,761 IOTA, and that transaction is actually pretty close) and it will confirm. No balances will be changed, so it is pretty pointless.
(As you can see, such bundles are tagged with yellow "equals sign" by thetangle.org).
About the motivation I can only speculate. Either somebody is trying to troll the system, or somebody is trying to artificially inflate the amount of IOTA spent via the network (but I don't know any statistics of that kind that would not filter out such bundles).