Warren Buffett's Berkshire Hathaway posted a 4% drop in operating earnings to $11.2 billion in its first earnings report since the legendary investor revealed he plans to step down as CEO. Second-quarter earnings fell as slimmer insurance underwriting profits offset higher income from BNSF Railway, Berkshire Hathaway Energy, and the manufacturing, service, and retailing division.Another key driver of the decline was an$877 million foreign currency exchange loss tied to non-dollar debt — a sharp swing from ...