Clarifying multiple accounts
I have an iphone 11 and a macbook pro and I would like to use both to access photos via iCloud. My phone is signed in with a username@mac.com ID and my macbook with a username@gmail.com ID. both devices list the others (ie, the iphone lists both the iphone 11 and the macbook pro) under the settings-apple id info, so it would appear they are the same despite the difference in username. I would like to merge the two and end up with a single apple ID. Can I do this without losing my iTunes library and photos?
Thanks,
MacBook Pro 15", macOS 10.15