title: Pandas MultiIndex: Divide all columns by one column
body: <p>I have a data frame <code>results</code> of the form</p>
  
  <pre><code>                  TOTEXPPQ      TOTEXPCQ     FINLWT21
  year quarter                                         
  13   1        9.183392e+09  5.459961e+09  1271559.398
       2        2.907887e+09  1.834126e+09   481169.672
  </code></pre>
  
  <p>and I was trying to divide all (the first two) columns by the last one. My attempt was </p>
  
  <pre><code>weights = results.pop('FINLWT21')
  results/weights
  </code></pre>
  
  <p>But I get </p>
  
  <pre><code>ValueError: cannot join with no level specified and no overlapping names
  </code></pre>
  
  <p>Which I don't get: There are overlapping names in the index:</p>
  
  <pre><code>weights.head()
  year  quarter
  13    1          1271559.398
        2           481169.672
  </code></pre>
  
  <p>Is there perhaps a better way to do this division? Do I <em>need</em> to reset the index?</p>