Done and dusted
Definition 1 of 1
Pro Tip 1/3British Origin
The phrase is primarily used in the UK and Australia, so it might not be well understood by American English speakers. 
Once we tally up these figures, our work will be done and dusted.
Pro Tip 2/3Informal Speech
It's best used in casual or informal settings, as it's an idiomatic expression not suitable for formal writing. 
The team cheered, saying their training was done and dusted.
Pro Tip 3/3Complete Finality
It implies that not only is the task finished, but it also has been checked and needs no further attention. 
She submitted her essay, confident it was done and dusted.