Apple shares declined 1% in after-hours trading on Monday after the communications hardware firm said its chief executive, Tim Cook, would step down after nearly 15 years at the helm of the world's second most-valuable company. The decision by Cook, 65 years old, ​to step aside in favor of longtime Apple hardware chief John Ternus took Wall Street by surprise and will ‌raise questions about whether the new chief can maintain the brisk pace set by his predecessor.