Spanish banking giant BBVA is switching its 110,000 staff to use Google's range of enterprise software.
The deal is the biggest that the search giant has signed with one company for its cloud-computing services, where software is offered as a service via the internet.
The bank told the BBC it would use Google's tools only for internal communication.
But the deal can be seen as a breakthrough in corporate adoption.
Banking - with its high security needs and strict regulations - was always considered to be one of the last industries to accept cloud-computing.
BBVA's director of innovation, Carmen Herranz, stressed that all customer data and other key banking systems would "stay in our own data centres" and be completely separate from the cloud solution.
The bank would use Google applications like email, calendar, docs, chat, video conferencing and other collaboration tools to "achieve a cultural change" and get "the whole company working together" across the 26 countries where BBVA is based.
Ms Herranz said the project - with roll-out across all employees to be complete by the end of the year - was not about saving cost.
"The main goal is to promote innovation and making decisions and increase productivity. We are in a challenging market and need to make faster and more accurate decisions... and eliminate duplication," Ms Herranz told the BBC.
Also driving the change was the increasing mobility of the bank's workforce. A lot of the bank's computing needs had moved to smartphones, tablets, laptops and computers at home, she said.
Jose Olalla, chief information officer at BBVA, said because workers now had "access [to] the information they need at any time from any internet-connected device, anywhere in the world, [they] will be able to be more flexible and mobile".
BBVA is one of Spain's largest banks.
It is also the largest provider of financial services in Mexico, and has a large presence in the south of the United States. >>Read more