Two week shutdown during production times are called TLOs (temporary layoffs) in UAW plants. (It can be up to two weeks, but not more). By contract, the union employees are paid 90% of their normal rate to go home; they don't even have to file for unemployement during that time as the company pays that 90%. They can also only do so many TLOs in any given period. It's been 20 years since I worked at Ford, but IIRC, it's a max of 2 weeks in any three month period. It could be slightly different now, but I doubt it's changed much; the Union will NEVER give up a benefit once it's been achieved.
There is some company savings to be had ... 10% labor savings for those TLO'd, and of course all the operational costs (mostly the massive electric bill is reduced) as the plant goes dormant. Sometimes the production folks are "laid off" and the maintenance crews work on major projects.
If the company needs to reduce costs past that, what they will do is a workforce rebalance; they will adjust the line speed to run slower, reduce headcount on the line, and each person has a larger piece of the pie to build during their alloted line time. It's basic industrial engineering math. Slowing the line increases the TAKT time, and allows more work per work station, albiet producing less vehicles per hour with less heads on the line.