From generous pay and benefits to stronger job security, the U.A.W. Workers union won significant concessions in tentative settlements that have ended their strikes against Detroit’s three automakers. Now, General Motors, Ford and Stellantis are facing sharply higher labor costs, estimated by some analysts at exceeding $1 billion per year, per company. The automakers said they will try to absorb those cost increases through expense reductions and efficiencies while still aiming to post strong enough profits to please Wall Street.