Discover Financial Services (DFS) 10-Q 2007 Q3 Quarterly report

Exhibit 18

October 12, 2007

Discover Financial Services

2500 Lake Cook Road

Riverwoods, IL 60015

Dear Sirs/Madams:

At your request, we have read the description included in your Quarterly Report on Form 10-Q to the Securities and Exchange Commission for the quarter ended August 31, 2007, of the facts relating to the change in the goodwill annual impairment testing date. We believe, on the basis of the facts so set forth and other information furnished to us by appropriate officials of the Company, that the accounting change described in your Form 10-Q is to an alternative accounting principle that is preferable under the circumstances.

We have not audited any consolidated financial statements of Discover Financial Services and its consolidated subsidiaries (the “Company”) as of any date or for any period subsequent to November 30, 2006. Therefore, we are unable to express, and we do not express, an opinion on the facts set forth in the above-mentioned Form 10-Q, on the related information furnished to us by officials of the Company, or on the financial position, results of operations, or cash flows of the Company and its consolidated subsidiaries as of any date or for any period subsequent to November 30, 2006.

Yours truly,

/s/ Deloitte & Touche LLP

Chicago, Illinois