Ctrl-space - default format.

Took me 3 minutes to find in Word Help

Also available:

CTRL+D
Change the formatting of characters (Font command, Format menu)
SHIFT+F3
Change the case of letters
CTRL+SHIFT+A
Format letters as all capitals
CTRL+B
Apply bold formatting
CTRL+U
Apply an underline
CTRL+SHIFT+W
Underline words but not spaces
CTRL+SHIFT+D
Double-underline text
CTRL+SHIFT+H
Apply hidden text formatting
CTRL+I
Apply italic formatting
CTRL+SHIFT+K
Format letters as small capitals
CTRL+EQUAL SIGN
Apply subscript formatting (automatic spacing)
CTRL+SHIFT+PLUS SIGN
Apply superscript formatting (automatic spacing)
CTRL+SPACEBAR
Remove manual character formatting
CTRL+SHIFT+Q
Change the selection to the Symbol font