It is composed of "core capital", which consists primarily of common stock and disclosed reserves (or retained earnings), but may also include non-redeemable non-cumulative preferred stock.
It's non-cumulative, meaning that if he were to take no vacation time in 2016/17, he wouldn't be entitled to 12 weeks' vacation in 2017/18 -- just six.
The post-deferral losses of non-cumulative preferred stock are comparable only to losses of cumulative preferred stock deferrals followed by debt defaults.