Banks and brokers are in line to share between $150 million and $175 million in fees for steering BG Group's £54.8 billion takeover by Royal Dutch Shell, one of 2015's largest and most lucrative M&A deals, according to a newly-published document.

The size of the potential fee windfall from both sides was revealed for the first time since the recommended takeover was announced on April 8, in a document released by BG on December 22.