All shares and all certificates representing Unicom Corporation or Commonwealth Edison Company were required to be exchanged for Exelon Corporation common stock. Each one share of Unicom (or Commonwealth Edison) received 0.875 shares of Exelon common stock.

Historical share prices of Unicom Corporation and Commonwealth Edison Company common stock are available here.

Historical dividend information is available here.

PECO Energy shares were not required to be exchanged, but continued to trade under Exelon’s name. Certificates for common shares of PECO Energy Company or Philadelphia Electric Company (provided the account is still open) are fully tradable as Exelon common stock.

Historical share prices of PECO Energy Company and Philadelphia Electric Company common stock are available here.

Historical dividend information is available here.

On March 12, 2012, Exelon Corporation acquired Constellation Energy Group, Inc. All shares and all certificates representing Constellation Energy Group or Baltimore Gas and Electric Company were required to be exchanged for Exelon Corporation common stock. Each one share of Constellation Energy Group (or Baltimore Gas and Electric Company) received 0.93 shares of Exelon common stock.

Historical share prices of Constellation Energy Group and Baltimore Gas and Electric Company are available here.

Historical dividend information is available here.

Report of Organization Actions Affecting Cost Basis of Securities is available here.

On March 23, 2016, Exelon acquired Pepco Holdings Inc. (PHI). Each share of PHI (former ticker POM) was converted into the right to receive a cash payment of $27.25 per share (the Cash Payment). The Cash Payment is fully taxable as income in 2016 regardless of when the holder tendered shares for payment.

PHI was formed on August 2, 2002 when Potomac Electric Power Company (PEPCO) acquired Conectiv Power Delivery (Conectiv). Holders of Conectiv common stock (former ticker CIV) and Conectiv Class A common stock (former ticker CIV.A) were given the opportunity to elect to receive either cash or shares of PHI common stock in exchange for their Conectiv shares.

Holders who elected to receive cash for the Conectiv shares received $25 for each share of Conectiv common stock and $21.69 for each share of Conectiv Class A common stock.

Holders who elected to receive shares of PHI common stock received 1.28205 shares of PHI common stock for each share of Conectiv common stock and 1.11227 shares of PHI common stock for each share of Conectiv Class A common stock.  

Holders who did not make an election received 0.84882 shares of PHI common stock and $8.44792 in cash for each share of Conectiv common stock and 0.73642 shares of PHI common stock and $7.32942 in cash for each share of Conectiv Class A common stock. 

Holders of PEPCO common stock were required to exchange their shares for PHI common stock. Each share of PEPCO common stock was exchanged for one share of PHI common stock.

Historical prices for PHI common stock from 2002 through 2016 as well as for PEPCO common stock from 1990 through 2002 are provided here.

Historical prices for PEPCO common stock from 1952-1989 are provided here.

Historical prices for Conectiv common stock and Conectiv Class A common stock are provided here:

Conectiv was formed in March 1998 when Delmarva Power & Light Company merged with Atlantic Energy, Inc., the parent company of Atlantic City Electric Company.

Each share of Delmarva Power & Light Company common stock (former ticker DEW) received one share of Conectiv common stock. Each share of Atlantic Energy Inc. common stock (former ticker ATE) or Atlantic City Electric common stock received 0.75 shares of Conectiv common stock and 0.125 shares of Conectiv Class A common stock.

Historical prices for Delmarva Power & Light Company are provided here:

Historical prices for Atlantic Energy Inc and Atlantic City Electric Company are provided here:

The dividend history of PHI and its predecessor companies is provided here:

In May 2013 all outstanding preferred shares of PECO Energy Company were called for redemption. Specific details are available here.

Exelon's PECO Announces Redemption of Preferred Stock

Report of Organization Actions Affecting Cost Basis of Securities is available here.