Hi, I'm looking at a multi-city ticket that has segments on United, ANA, Cathay, and an Alaska flight operated by American. This is all bookable directly on United.com as one big multi-city itinerary.

My question is: How does mileage earning work on something like this? Would all the flights credit to my UA account somehow? Or just the UA and ANA flights? Can I put in a different mileage account number for each segment (eg: credit to my BA account for the Cathay and Alaska/AA segments, and credit to my UA account for the UA/ANA segments)? Or, would I not be able to earn on the Cathay and Alaska/AA segments? Would you just ask at check-in for each segment to put in the appropriate number, or do it over the phone with UA beforehand?

Thanks for any information.
Chris