Asset allocation is all about allocating assets to asset classes, most of which can be thought of has having sub-classes that therefore also receive allocations. In the case of the stock/equity asset class, for example, most people consider the sub-classes to be US and International (though some people, might consider the sub-classes to be US, Developed International and Emerging Markets).
In the case of the fixed income asset class, many people consider the sub-classes to be Nominal Bonds and Real Bonds. Others, such as myself, consider the sub-classes to be: Stable Value, Nominal Bonds and Real Bonds. I consider my TIAA Traditional to be part of my Stable Value allocation (along with US EE Savings Bonds).
There is no perfect way to do this -- just a way that makes sense for you. I.e. realizing yourself what defines each class and sub-class and why you have a particular allocation to each. To my way of thinking, Stable Value is different from Nominal Bonds and Real Bonds because the principal value is unaffected by changes in interest rates. This does not make Stable Value safer than Nominal Bonds or Real Bonds -- just different (and therefore adding additional diversification to a portfolio), especially, as some have pointed out, if you have the illiquid form of TIAA Traditional.
Overall then the allocation to stock/equity is unaffected by the sub-allocations to fixed income. As a first approximation, 60/40 portfolio is a 60% stock/equity regardless of how the 40% fixed income is deployed (with the huge proviso that all the fixed income investments are SAFE -- e.g. no high-yield "bonds"). In my own case, I am 25% fixed income and have recently shifted my sub-allocation to eliminate Real Bonds and minimize Nominal Bonds in favor of loading up on Stable Value (TIAA Traditional in its liquid form) -- but this has not affected the rest of my allocation at all.
As others have posted, beyond this first approximation it is possible to think of sub-class allocations causing shifts in asset class allocations -- e.g. increasing the small and value stock/equity sub-classes IN ORDER TO REDUCE the overall stock/equity allocation (and hence increase the fixed income allocation). A similar argument can be made for multi-asset-class portfolios where an allocation to a third (or even fourth and fifth) asset class (such as collateralized commodities future, real estate such TIAA Real Estate Account and the like) affects the allocations to stock/equity and fixed income. But there may be no need for you to go into those weeds ...