A whale of a chance

Please tell me what's the meaning of "A whale of a chance"? I've seen it in "Richard Ellsworth Savage" from "The Big Money" by Dos Passos.

Because the whale is the largest animal on earth, "a whale of a [thing]" is an idiom meaning "a very big - and usually very good - [thing]". You can have a "whale of a good time", "a whale of a joke", and so on.(VSD)

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