if a piece of information is anybody's guess, no one knows it.

Why Becky left is anybody's guess.

'So what's going to happen now?' 'That's anybody's guess.'

• be as easy as abc
• be as easy as falling off a log
• be as easy as pie
• be as fast as all get out
• be as [fast/hot/thin etc.] as all get out
• be as fit as a fiddle
• be as flat as a pancake
• be as fresh as a daisy
• be as full as a boot
• be as full as a tick
• be as gentle as a lamb
• be as good as gold
• be as good as new
• be as good as word
• be as good as your word
• be as happy as a sandboy
• be as happy as Larry
• be as hard as nails
• be as high as a kite
• be as honest as the day
• be as honest as the day is long
• be as hot as all get out
• be a sight for sore eyes
• be a sign of the times
• be as keen as mustard