At the time I was a college dropout with a pretty bad attitude but I needed a job and I wasnt afraid to work long boring hours and so I got a job stocking shelves at a walmart near my parents house. It was a mind numbing job but it actually paid ok at the time (12$ hour, I was in orlando, this was 2008ish).
After simply showing up on time and doing my job properly for just a few months I was told that if I wanted I could take on more responsibilities. I met with our store manager who showed me stats about how walmart really likes to promote from within and that if I stuck with it I could get to be an assistant manager in a store in just a few years. The store manager telling me this had a GED and had worked at walmart for 15 years. He told me his salary was "close to 200k." I couldn't believe it.
In my few years working at that store I saw several people get promoted from shelf stocker to department supervisor to assistant manager. One of those people is a store manager at a store in Georgia now. I left my job at walmart with a pretty evolved opinion of the place. For a long time I told people who were directionless and worried about what their future would look like to seriously consider working at walmart and to make it clear to their bosses they wanted to move up.
There were other benefits back then that were pretty solid. I worked with a couple of women who got a lot of their tuition reimbursed. Both of whom are nurses now. I really did feel like if you could put up with some of the BS you get working at walmart you could actually get something good out of the experience for yourself.
Anyway this was a long rambley way of saying that at least in 2008-2010 when I worked at walmart they really valued promoting from within.
Oh final note: there were lots of programs like the tuition reimbursement one tha I was told about when I was hired but assumed there was some catch or some way that it wouldn't work out. The HR manager at my store told me once that some of these things just required you do sign up and that she was shocked how low the participation rates were.
AFAIK they've never had any issues with having enough people in their org either on the retail or corporate side who want to be in leadership roles.