To earn this achievement, when you clear the scenario your railway assets have to exceed other property and stock by 15%. While technically cash is an asset, it is not counted for this achievement as such.
Start a scenario on Isolated Region and build a resource center on the north edge, east of the centerline marker on the map. You will be building a Maglev rail to the west of the centerline and blocking the one path on this map where a Maglev train can fit will cause difficulties. Wait until you have around $9 billion in cash, and save the scenario so you can reload if you make a mistake.
Open the Market menu and use to go to the Bank submenu. Use to change the loan amount. You will need to open multiple loans until you are at $9.99 billion. DO NOT GO OVER THIS AMOUNT! Once you have enough money, press to close the Market and press once to go to the Project menu. Press , and then use and to line up the Maglev at a permitted spot (the line will turn blue.) Press to build it, and unpause time by pressing .
It takes just over 4 months to build it, so the only tricky part is to not exceed $10 billion while waiting. Once you are back up to $6-7 billion, open the Station menu and build Materials Yards over about 2/3 of your convenience stores. You need to watch your cash and aim for stability...you don't want to lose money, but you don't want to increase any more either. Your may have to adjust this several times while waiting for the Maglev to be constructed.
Once construction is complete, you are ready to clear the scenario. Open the Report menu and use to go to the Balance Sheet. On the right under Total Assets, look at the Subsidiaries line. These are your convenience stores, and are likely worth far more than your bullet train. Build Materials Yards on top of them until you are down to about $5 billion in Subsidiaries, then go to the Market menu and take out enough loans to reach $10 billion. The scenario will clear and you will unlock the achievement (it unlocks after updating the leaderboards if you choose to do so).