Is it considered usury if I borrow 100 million from the bank, where 50 million are waived, and the remaining 50 million are to be paid back, becoming 100 million over twenty years, knowing that I will return 100 million in exchange for the 100 million I borrowed?

Returning a debt with an increase is usury (riba). The scenario described implies a usurious loan, half of which was waived, and the other half was repaid with usurious interest. Dealing in usury is one of the gravest sins, forbidden by the Qur'an, the Sunnah (definition), and scholarly consensus.