All the banks in the list contain substantial wealth management operations.

The rating changes are as follows:

“The downgrades and revised outlooks reflect our view of the significant pressure on large complex financial institutions' future performance due to increasing bank industry risk and the deepening global economic slowdown,” S&P said in a statement.

“We are raising our overall assessment of bank industry risk and believe there will be more volatility in funding markets,” it said.

Banks worldwide have reported more than $745 billion of writedowns and losses since the credit crisis began, according to data compiled by Bloomberg.