St Andrews is currently 5th for graduates going on to do something related to their area of study (for Maths, 20th), (for Philosophy 1st-Oxford was second), and 15th for going to have 'success' in general (for Maths, joint 11th), (for Philosophy 2nd-Exeter was first). The Complete University Guide.
Only 12% of St Andrews Philosophy graduates aren't doing something that uses that degree. For Mathematics, it's 20% but that's better than Cambridge (22%).
If you're interested in banking though, you'd switch to at least a joint honours with Economics surely, for which St Andrews graduates are joint 15th for success in general (above Bristol and Manchester), and joint 18th for related activity. (above Manchester, LSE, and UCL).