line (one's) (own) pocket(s)

To make a large amount of money for oneself in a way that is considered greedy or dishonest. The phrase typically implies that one is prioritizing making money above some other, more admirable goal. He doesn't care about creating some digital utopia—he's just trying to line his own pockets. This new contract is going to line our pockets for years.

line your pockets

COMMON If someone lines their pockets, they make a lot of money in a dishonest or unfair way. He has been lining his pockets for 27 years while his country has been in poverty. Morris lined his own pockets with most of the cash, buying a Mercedes Benz, jewelry and paying off credit card debts as well. Note: You can also say that someone lines another person's pockets. This is a government that ignores the needs of the majority in order to line the pockets of the favoured few.