Done by trains with "unlimited" return after unplanned departure in USA (6,9)

I believe the answer is:

double indemnity

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'return after unplanned departure in usa' is the definition.
I can't tell whether this definition defines the answer.

'done by trains with unlimited' is the wordplay.
'trains with' indicates anagramming the letters (I've seen 'trained' mean this (to train can mean to grow something into a shape)).
'done'+'by'='doneby'
'doneby' anagrammed with 'unlimited' gives 'DOUBLE INDEMNITY'.

Can you help me to learn more?

(Another definition for double indemnity that I've seen is " Film".)

I've seen this clue in The Independent.

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