This trophy is earned when you have
1,000,000 units saved up in your bank. This is not cumulative based on what you've earned throughout the game. The one million units must be sitting unspent in your bank account in order to get the trophy.
Units can be earned throughout the game by selling inventory items to traders or galactic terminals liberally scattered throughout the universe. You can also obtain a few extra units from "stock transfer" terminals randomly found in alien outposts or space stations.
At this time, you CAN NOT earn units through the sale/trade of ships or multi-tools.
Rarer (and thus more valuable) items and elements tend to be found on planets with more extreme weather conditions. For a quick fix, though, I used the Bypass Chip idea described in this Polygon article to earn a solid chunk of my units, even in more temperate solar systems:
http://www.polygon.com/2016/8/10/12421926/no-mans-sky-quick-...Good luck!