A job manual is something that each assistant should have handy and kept current at all times, not created solely when you are transitioning out of your position. It's a living reference for you, your employer and sometimes even other coworkers or household staff.
At one of my positions we called it the "Best of the Best Binder," and I couldn't agree more with that title. The manual allows whoever has it all information needed to perform the main functions required.
I recommend keeping the master copy of your manual on a cloud storage site, such as Dropbox or Evernote. It should be broken down into folders for each chapter so you can share portions as necessary when your job requires. Always get approval from your employer before sharing chapters with others. You should set aside time on a regular basis to keep it up to date so the information is current and relevant.
Here are some ideas for chapters:
I do not recommend writing down passwords. One workaround for this is to have 3-4 code words for passwords that you would use for certain types of logins. An example is using a password code word that you call "Normal" for less sensitive sites, such a shopping, restaurant reservations and beauty services. All of the "Normal" passwords would be the same. You could use a password code word called "Financial" that could be shared with accountants and other financial service people that are used for banking and investment sites. Again, all "Financial" passwords would be the same. If one of your passwords has an edit (ex: one character needs to be removed), then add a tip next to the code word. An example would be "Normal- delete the last character."
I also recommend creating other binders as your position evolves or as your unique situation demands. For example, if you are a Family Assistant, you could create a binder focused solely on the children. In one of the kid's binders I created, I included chapters for all excursion ideas broken down by activity (ex: swimming, museums, playgrounds, etc.), kid-friendly restaurants, emergency contact numbers, a general contact list and an allergy list. If you are a House or Estate Manager, you would need a separate manual focused solely on maintaining the property.
Lastly, I recommend always keeping a hard copy of your binder on you at all times. As assistants, we are often required to be on the go a majority of the time, and sometimes technology fails us. Imagine you need to look up information and your iPhone battery dies or your hotspot can't get a signal. Your binder will feel like a lifesaver in those situations.
Do you maintain a job manual? Please share your best practices in the comments below!