SoftBank Group Corp., under pressure to raise capital after record losses in its investment business, is unloading part of its stake in wireless carrier T-Mobile U.S. Inc. in a $21 billion (¥2.24 trillion) deal.

The transaction, along with a plan to sell a 5 percent stake in its Japanese wireless subsidiary, is part of a broader $42 billion push by SoftBank to unload assets to finance stock buybacks and pay down debt. Masayoshi Son, the company’s founder, is dealing with steep losses in his Vision Fund after writing down the value of investments in the sharing economy from WeWork to Uber Technologies Inc.

The investment giant will now turn its attention to other assets in its portfolio and may pursue an outright sale of part of its stake in Chinese e-commerce giant Alibaba Group Holding Ltd. Son has said $11.5 billion raised from issuing contracts to sell stock in Asia’s largest corporation was a first step toward unwinding more of its holdings.