The Financial Review reports that Westpac "is planning a partial sharemarket float of its investment management arm, BT Financial Group."The newspaper reports that Westpac is likely to float 45 per cent and thus retain a 55 per cent stake.A perceived need to offer direct ownership in BT to staff, and in particular to key investment staff, is reported to the bank's rationale for a float. The prospect that BT would trade at a higher multiple on the ASX than for the bank's own stock may also be a factor.Westpac bought BT in 2002 from Principal Financial, having failed to buy BT when sold by Deutsche Bank in 1999. (Westpac paid about half what Principal paid at the height of the late 1990s equities boom).The AFR speculates that Westpac will value BT at "close to $1 billion".