Read the most recent 10Q and then you'll understand (ZION, rated SELL)
Zions Bank provides a liquidity facility (“Liquidity Facility”) for a fee to Lockhart Funding, LLC (“Lockhart”), a qualifying special-purpose entity (“QSPE”) securities conduit. " Lockhart purchases floating rate U.S. Government and AAA-rated securities with funds from the issuance of commercial paper. Zions Bank also provides interest rate hedging support and administrative and investment advisory services for a fee. Pursuant to the Liquidity Facility contract, Zions Bank is required to purchase securities from Lockhart to provide funds for Lockhart to repay maturing commercial paper upon Lockhart’s inability to access the commercial paper market, or upon a commercial paper market disruption as specified in governing documents for Lockhart. Pursuant to the governing documents, including the liquidity agreement, if any security in Lockhart is downgraded below AA-, Zions Bank must either 1) place its letter of credit on the security, 2) obtain credit enhancement from a third party, or 3) purchase the security from Lockhart at book value. Zions Bank may incur losses in the event it is required to purchase securities from Lockhart because it would record any repurchased securities at fair value, which may be below the book value that would be paid to Lockhart."