Capital Changes Report will allocate ABT before and value both Company's , Just like Hospira spinoff 10 or so years ago ~ 15% was basis allocated. Now Post Hospira ABT gets spun off they value both companys. Until we know better information, I think we will get 1 old ABT with 1 new share of New ABT and 1 New Share of Abbvie if they value the Same. Or the Basis gets allocated a % of each new company Market value to the whole of both Company's.
There will be a section on the ABT website that tll you how to handle the spinoff , similar to hospira .