Carmakers’ Captives Show Reasons to Be Fearful

Bets on the world’s biggest car companies look a bit less safe as the U.S. market confronts slowing sales, an obsession with trucks and ballooning numbers of used cars.

Bonds of captive auto-finance companies like Ford Motor Credit Co., Toyota Motor Credit Corp., General Motors Financial Co. and Daimler AG’s financing subsidiary have been trading more like their parents in recent months. These units, essentially enablers of purchases by millions of consumers, have sold $78 billion of debt so far this year — the most in a decade for that period.