Pending Merger with NorthWestern	6 Months Ended
Jun. 30, 2026
Business Combination, Asset Acquisition, Transaction between Entities under Common Control, and Joint Venture Formation [Abstract]
Pending Merger with NorthWestern	(14) Pending Merger with NorthWestern On August 18, 2025, we entered into an Agreement and Plan of Merger (the “Merger Agreement”), with NorthWestern and Merger Sub. The Merger Agreement provides for Merger Sub to merge with and into NorthWestern (the “Merger”), with NorthWestern continuing as the surviving entity and a direct wholly owned subsidiary of Black Hills Corporation, which will assume a new corporate name, Bright Horizon Energy Corporation, as the resulting parent company of the combined corporate group. At the effective time of the Merger (the “Effective Time”), each share of common stock of NorthWestern, par value $0.01 per share, issued and outstanding as of immediately prior to the Effective Time will be converted into the right to receive 0.98 validly issued, fully paid and non-assessable shares of our common stock, par value $1.00 per share (or cash-in-lieu of fractional shares thereof), in each case upon and subject to the terms and conditions of the Merger Agreement. The Merger Agreement, which was unanimously approved on August 18, 2025, by both the board of directors of Black Hills Corporation and the board of directors of NorthWestern, provides for a tax-free, all-stock business combination of Black Hills Corporation and NorthWestern upon the terms and subject to the conditions set forth therein. Such conditions include, among other things, clearance under the HSR Act, consent of the FCC, approval from each company's shareholders, and regulatory approvals, including approval from the SDPUC, NPSC and MPSC, as well as the FERC. To date, the status of these matters is as follows: • In October 2025, we filed joint applications for approval with the MPSC, NPSC, and SDPUC. o In March 2026, we reached a settlement agreement with all intervening parties in Nebraska. On May 19, 2026, the NPSC approved the merger. o In April 2026, we reached a settlement with the SDPUC Staff, which was filed with the SDPUC. On June 24, 2026, the SDPUC approved the merger. o In April 2026, we reached settlements agreements with several parties in Montana, which were filed with the MPSC. Hearings before the MPSC occurred during the second quarter of 2026. The settlement agreements are subject to approval by the MPSC. • On December 22, 2025, we filed a joint application with the FERC. The initial public comment period closed on January 20, 2026. On May 29, 2026, we received approval for the Merger from the FERC. • On January 30, 2026, the Form S-4, which contains a joint proxy statement/prospectus for the Black Hills Corporation and NorthWestern, was publicly filed with the SEC. On February 6, 2026, the Form S-4 was declared effective by the SEC. On April 2, 2026, shareholders from both Black Hills Corporation and NorthWestern voted to approve the proposed all-stock merger. • On March 19, 2026, we filed an application for clearance under the HSR Act. The waiting period under the HSR Act was completed on April 20, 2026, satisfying a U.S. antitrust condition to closing. We anticipate the transaction closing by year-end 2026, subject to the satisfaction of certain closing conditions and remaining regulatory approval from the MPSC as mentioned above.

Pending Merger with NorthWestern

6 Months Ended

Jun. 30, 2026

Business Combination, Asset Acquisition, Transaction between Entities under Common Control, and Joint Venture Formation [Abstract]

Pending Merger with NorthWestern

(14)

Pending Merger with NorthWestern

On August 18, 2025, we entered into an Agreement and Plan of Merger (the “Merger Agreement”), with NorthWestern and Merger Sub. The Merger Agreement provides for Merger Sub to merge with and into NorthWestern (the “Merger”), with NorthWestern continuing as the surviving entity and a direct wholly owned subsidiary of Black Hills Corporation, which will assume a new corporate name, Bright Horizon Energy Corporation, as the resulting parent company of the combined corporate group. At the effective time of the Merger (the “Effective Time”), each share of common stock of NorthWestern, par value $0.01 per share, issued and outstanding as of immediately prior to the Effective Time will be converted into the right to receive 0.98 validly issued, fully paid and non-assessable shares of our common stock, par value $1.00 per share (or cash-in-lieu of fractional shares thereof), in each case upon and subject to the terms and conditions of the Merger Agreement.

The Merger Agreement, which was unanimously approved on August 18, 2025, by both the board of directors of Black Hills Corporation and the board of directors of NorthWestern, provides for a tax-free, all-stock business combination of Black Hills Corporation and NorthWestern upon the terms and subject to the conditions set forth therein. Such conditions include, among other things, clearance under the HSR Act, consent of the FCC, approval from each company's shareholders, and regulatory approvals, including approval from the SDPUC, NPSC and MPSC, as well as the FERC. To date, the status of these matters is as follows:

•

In October 2025, we filed joint applications for approval with the MPSC, NPSC, and SDPUC.

In March 2026, we reached a settlement agreement with all intervening parties in Nebraska. On May 19, 2026, the NPSC approved the merger.

In April 2026, we reached a settlement with the SDPUC Staff, which was filed with the SDPUC. On June 24, 2026, the SDPUC approved the merger.

In April 2026, we reached settlements agreements with several parties in Montana, which were filed with the MPSC. Hearings before the MPSC occurred during the second quarter of 2026. The settlement agreements are subject to approval by the MPSC.

•

On December 22, 2025, we filed a joint application with the FERC. The initial public comment period closed on January 20, 2026. On May 29, 2026, we received approval for the Merger from the FERC.

•

On January 30, 2026, the Form S-4, which contains a joint proxy statement/prospectus for the Black Hills Corporation and NorthWestern, was publicly filed with the SEC. On February 6, 2026, the Form S-4 was declared effective by the SEC. On April 2, 2026, shareholders from both Black Hills Corporation and NorthWestern voted to approve the proposed all-stock merger.

•

On March 19, 2026, we filed an application for clearance under the HSR Act. The waiting period under the HSR Act was completed on April 20, 2026, satisfying a U.S. antitrust condition to closing.

We anticipate the transaction closing by year-end 2026, subject to the satisfaction of certain closing conditions and remaining regulatory approval from the MPSC as mentioned above.