Utilize the input text as a context reference, choose the right relationship between Willis Group and insurance broker from the options. Options: product/material produced, manufacturer, distributed by, industry, position held, original broadcaster, owned by, founded by, distribution format, headquarters location, stock exchange, currency, parent organization, chief executive officer, director/manager, owner of, operator, member of, employer, chairperson, platform, subsidiary, legal form, publisher, developer, brand, business division, location of formation, creator.

Last week insurance broker Willis Group signed an $18 billion agreement with Towers Watson & Co to combine the companies in an all-stock deal with an implied equity value of about $18 billion.

Answer: industry