Highly Superior Autobiographical Memory (HSAM), or hyperthymesia, is a rare condition in which an individual remembers every single day of his or her life in precise detail.
Less than a hundred people in the world are believed to have perfect hyperthymesia. One of them is actress Marilu Henner. In 2012 she published a book about her memory (with tips for how to improve yours) called Total Memory Makeover: Uncover Your Past, Take Charge of Your Future.
(I’ve read it, by the way—it’s a worthwhile book if you’re interested in this topic.)