Ann: December 2017 Quarterly Report and Appendix 4C, page-15

It's actually not all that bad considering. That's 0.19% for the quarter, which is 0.76% annualised. Sure, lower than treasury bonds, but like Skelts said, you wouldn't want the whole pile in a higher interest/TD account.
More than likely, a fair chunk is earning ~2%, but another fair chunk is also in regular spending accounts not earning much at all.