Please read the following table in HTML format from a webpage and then answer the question in detail according to the table. Each table cell is defined by a <td> and a </td> tag. Each table row starts with a <tr> and ends with a </tr> tag. 'rowspan=m' and 'colspan=n' represents a cell spaning over 'm' rows and 'n' columns.

Webpage title:
List of best-selling singles
Table title:
15 million copies or more
Table:
<table id='hittask' contenteditable='False'>
<tr> <th colspan=1 rowspan=1 > Artist </th><th colspan=1 rowspan=1 > Single </th><th colspan=1 rowspan=1 > Released </th><th colspan=1 rowspan=1 > Sales (in millions) </th><th colspan=1 rowspan=1 > Source </th></tr>
<tr> <td colspan=1 rowspan=1 > Bing Crosby </td><td colspan=1 rowspan=1 > "White Christmas" </td><td colspan=1 rowspan=1 > 1942 </td><td colspan=1 rowspan=1 > 50 </td><td colspan=1 rowspan=1 >  </td></tr>
<tr> <td colspan=1 rowspan=1 > Elton John </td><td colspan=1 rowspan=1 > "Candle in the Wind 1997" / "Something About the Way You Look Tonight" </td><td colspan=1 rowspan=1 > 1997 </td><td colspan=1 rowspan=1 > 33 </td><td colspan=1 rowspan=1 >  </td></tr>
<tr> <td colspan=1 rowspan=1 > Mungo Jerry </td><td colspan=1 rowspan=1 > "In the Summertime" </td><td colspan=1 rowspan=1 > 1970 </td><td colspan=1 rowspan=1 > 30 </td><td colspan=1 rowspan=1 >  </td></tr>
<tr> <td colspan=1 rowspan=1 > Bing Crosby </td><td colspan=1 rowspan=1 > "Silent Night" </td><td colspan=1 rowspan=1 > 1935 </td><td colspan=1 rowspan=1 > 30 </td><td colspan=1 rowspan=1 >  </td></tr>
<tr> <td colspan=1 rowspan=1 > Bill Haley & His Comets </td><td colspan=1 rowspan=1 > "Rock Around the Clock" </td><td colspan=1 rowspan=1 > 1954 </td><td colspan=1 rowspan=1 > 25 </td><td colspan=1 rowspan=1 >  </td></tr>
<tr> <td class="highlighted"  colspan=1 rowspan=1 > Whitney Houston </td><td class="highlighted"  colspan=1 rowspan=1 > "I Will Always Love You" </td><td colspan=1 rowspan=1 > 1992 </td><td class="highlighted"  colspan=1 rowspan=1 > 20 </td><td colspan=1 rowspan=1 >  </td></tr>
<tr> <td colspan=1 rowspan=1 > Elvis Presley </td><td colspan=1 rowspan=1 > "It's Now or Never" </td><td colspan=1 rowspan=1 > 1960 </td><td colspan=1 rowspan=1 > 20 </td><td colspan=1 rowspan=1 >  </td></tr>
<tr> <td colspan=1 rowspan=1 > USA for Africa </td><td colspan=1 rowspan=1 > "We Are the World" </td><td colspan=1 rowspan=1 > 1985 </td><td colspan=1 rowspan=1 > 20 </td><td colspan=1 rowspan=1 >  </td></tr>
<tr> <td colspan=1 rowspan=1 > The Ink Spots </td><td colspan=1 rowspan=1 > "If I Didn't Care" </td><td colspan=1 rowspan=1 > 1939 </td><td colspan=1 rowspan=1 > 19 </td><td colspan=1 rowspan=1 >  </td></tr>
<tr> <td colspan=1 rowspan=1 > Baccara </td><td colspan=1 rowspan=1 > "Yes Sir, I Can Boogie" </td><td colspan=1 rowspan=1 > 1977 </td><td colspan=1 rowspan=1 > 18 </td><td colspan=1 rowspan=1 >  </td></tr>
<tr> <td colspan=1 rowspan=1 > Celine Dion </td><td colspan=1 rowspan=1 > "My Heart Will Go On" </td><td colspan=1 rowspan=1 > 1997 </td><td colspan=1 rowspan=1 > 18 </td><td colspan=1 rowspan=1 >  </td></tr>
<tr> <td colspan=1 rowspan=1 > Mariah Carey </td><td colspan=1 rowspan=1 > "All I Want for Christmas Is You" </td><td colspan=1 rowspan=1 > 1994 </td><td colspan=1 rowspan=1 > 16 </td><td colspan=1 rowspan=1 >  </td></tr>
<tr> <td colspan=1 rowspan=1 > Bryan Adams </td><td colspan=1 rowspan=1 > "(Everything I Do) I Do It for You" </td><td colspan=1 rowspan=1 > 1991 </td><td colspan=1 rowspan=1 > 15 </td><td colspan=1 rowspan=1 >  </td></tr>
<tr> <td colspan=1 rowspan=1 > John Travolta and Olivia Newton-John </td><td colspan=1 rowspan=1 > "You're the One That I Want" </td><td colspan=1 rowspan=1 > 1978 </td><td colspan=1 rowspan=1 > 15 </td><td colspan=1 rowspan=1 >  </td></tr>
</table>
Question:
How many copies did Whitney Houston's best-selling single sell?
Answer:
"I Will Always Love You" became the best-selling single by an artist with 20 million copies sold.