struct MyDecodable: Decodable {
    var id: Int64
}

let str = "{\"id\":1000000000000000070}"
let data = str.data(using: .utf8)!
let decodable = try! JSONDecoder().decode(MyDecodable.self, from: data)

let int64 = number.int64Value
let recreatedNumber = number is NSDecimalNumber ? NSDecimalNumber(value: int64) : NSNumber(value: int64)
guard recreatedNumber == number else {
    throw DecodingError.dataCorrupted(DecodingError.Context(codingPath: self.codingPath, debugDescription: "Parsed JSON number <\(number)> does not fit in \(type)."))
}