Erik McGregor / Contributor / Getty Images Key TakeawaysBlackRock and Morgan Stanley agreed to buy TC Energy's Portland Natural Gas Transmission System in a deal worth $1.14 billion.The move comes not long after BlackRock agreed to buy Global Infrastructure Partners for approximately $12.5 billion in January, as the world's largest asset manager expands its focus on infrastructure.TC Energy CEO Francois Poirier said that the deal was part of the Canadian company's effort to boost its balance sheet by selling off assets.