There used to be the "Windows tax" that the rest of Microsoft had to pay[1], now I guess that there is the "Rest-of-Microsoft tax" that Windows has to pay.
[1] https://www.ft.com/content/9e09d082-b5d3-11e3-a1bd-00144feab...
[1] https://www.ft.com/content/9e09d082-b5d3-11e3-a1bd-00144feab...
https://www.propublica.org/article/the-irs-decided-to-get-to...