UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d)

of the Securities Exchange Act of 1934

Date of report (Date of earliest event reported): February 19, 2015

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

The materials attached as Exhibit 99.1 relating to a potential settlement of Union Electric Company’s (doing business as Ameren Missouri, “Ameren Missouri”) pending rate case before the Missouri Public Service Commission were inadvertently disclosed. There can be no assurance that a settlement will be reached, and Ameren Missouri and Ameren Corporation do not presently intend to make any further public statement with respect to a settlement unless and until a settlement is reached.

This Current Report on Form 8-K is being furnished solely to satisfy the requirements of Regulation FD in light of the inadvertent disclosure. The information under Item 7.01 in this Current Report on Form 8-K will not be incorporated by reference into any registration statement or other document filed by Ameren Corporation or Ameren Missouri under the Securities Act of 1933, as amended, unless specifically identified therein as being incorporated by reference.

The furnishing of the information under Item 7.01 in this Current Report on Form 8-K is not intended to, and does not, constitute a determination or admission by Ameren Corporation or Ameren Missouri that the information under Item 7.01 in this Current Report on Form 8-K is material or complete, or that investors should consider this information before making an investment decision with respect to any security of Ameren Corporation or Ameren Missouri.

(d) Exhibits

This combined Form 8-K is being filed separately by Ameren Corporation and Union Electric Company (each a “registrant”). Information contained herein relating to any individual registrant has been filed by such registrant on its own behalf. No registrant makes any representation as to information relating to any other registrant.

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, each registrant has duly caused this report to be signed on its behalf by the undersigned thereunto duly authorized. The signature for each undersigned company shall be deemed to relate only to matters having reference to such company or its subsidiaries.

Date: February 20, 2015

Exhibit Index