take into one's confidence

Idioms  

1. Trust someone with a secret, as in She took me into her confidence and admitted that she was quitting next month. This idiom uses confidence in the sense of “trust,” a usage dating from the late 1500s.

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Example Sentences

My long experience in dealing with Colonial Governments had taught me that the surest way of achieving one’s object was to take into one’s confidence the leaders of the Opposition for the time being, convince them of the soundness and merits of the proposal, and induce them to adopt the scheme as a plank of their own policy.

From Project Gutenberg