Phrases that mean "I have no idea"

What phrases can be used interchangably with “I have no idea”?

I request two types of answers:

• Polite forms of saying it.

• Casual forms of saying it.

"I have no idea" seems simple and traditional. It doesn't show any emotions of the speaker in responding to the question.

Sometimes I feel that responding just "I have no idea/ I don't know" is not in a proper situation when I talk to my boss.

I also need a more playful expression when I say it ""I have no idea/ I don't know" to my friends.

Although I think it would be a relief for many bosses to just hear an honest 'I have no idea', these polite alternatives might work for you:

"Great question, let me look into it, and I'll get back to you."

"I'm not sure, let me look into it, and I'll get back to you."

Casually, you could say:

"I (really) have no clue."

If you want to emphasise the fact you really have no clue whatsoever, I think you could say:

"I cannot for the life of me understand why/how..."

• My English is far from perfect yet. Please check all my suggestions before using them ;)