A cousin passed away few years back with cancer. It wasn't sudden but wasn't expected either. (He was 37 and responding well to treatment). His wife was completely uninterested with regards to finances and bills. He was quite meticulous and wrote down every single account he owned, details like account number, login, password in an excel spreadsheet. It was a lot of help for her. I worry about security of such a syst…
Well, the best thing would be to write up all that, print it out, and put it in the same safe-deposit box that holds your will. Of all the storage media we have, paper is still the best proven for long-term retrieval.
Just make a couple copies, leave on in your desk, in your office, in your bedside table, with your lawyer. They are not secret documents, not something you have to lock up.