SharePoint: num of docs for each SPSite - PowerShell

$sites = Get-SPSite -Limit ALL
foreach($s in $sites){
  $ss = $s.AllWebs| % { $_.Lists } |?{$_.GetType().Name -eq "SPDocumentLibrary"}|%{$_.ItemCount}|Measure-Object -Sum
  "$($s.Url):$($ss.Sum)"
}