AltaGas on Wednesday entered in to an agreement to purchase WGL Holdings  (WGL) for C$8.4 billion ($6.4 billion) in an all-cash transaction.

The boards of directors of both the Calgary, Alberta-based energy infrastructure company and WGL have unanimously approved the deal, the statement said. AltaGas estimates its assets would grow to C$22 billion at the closing of the transaction.

WGL, which is the sole shareholder of Washington Gas Light, will continue to operate as a standalone utility, according to the statement. AltaGas said it plans to relocate its U.S. power business headquarters to Washington-based WGL's service region.

WGL's shares rose 3.45% to $81.50 in after-hours trading after the sale was announced. AltaGas shares, which are traded on the Toronto Stock Exchange, rose 0.57% to $33.32 on Wednesday.