Not just the US. iOS is also majority in all the anglosphere countries: uk, canada, australia

Then it has about 70% in japan. Europe is a bit lower, around 30-35%. And then the result of the world is android by a vast margin.

So in all the rich markets, iphone puts in a majority or good showing. Whereas android dominates at lower price points where the iphone doesn't compete.

http://gs.statcounter.com/os-market-share/mobile/japan

You can click around this site to see stats on different regions. Mind you I don't know where they source from.