AstraZeneca has explored a merger with Bristol Myers Squibb that would create one of the world's largest drugmakers, according to people familiar with the matter. The British pharmaceutical company has shown interest in its U.S. rival, which has a market capitalization of about $133 billion. A deal would give AstraZeneca a larger foothold in the U.S. market. The Financial Times reported the potential combination could be worth $400 billion. It is unclear whether talks are ongoing or will result in a transaction, the people cautioned. AstraZeneca declined to comment, and Bristol Myers Squibb could not immediately be reached for comment.