Now don't interpret my comments that because the banks own a stake in Qantas that it is a good buy. I am sure that they have made a lot of losses on various investments along the way to their major profits (CBA: $7B+, NAB: $5B+).
CBA and probably NAB also have other QF related liabilities on their books, such as aircraft (e.g. VH-EBL). What's an A330 worth, $200m?
CBA has something like $700b in assets under management, so it's pretty small fry in the grand scheme of things for them.