The country star revealed that he often feels pessimistic, but is forced to confront his negative attitude as Kidman won't tolerate his bad moods.
In an interview with GQ Australia, Urban explained: "Negativity and doubt are always creeping into my life and having to be kept at bay.
"Thankfully, Nic is great at calling me on it, and our marriage is at the stage where she doesn't have to say anything. I hear myself prattling on with negative crap and her loaded silence shuts me up."
The Voice Australia coach Urban went on to reveal why he and Kidman try to avoid speaking about their relationship publicly, adding: "We try to keep a sense of privacy around us, while acknowledging that Nic and I both inhabit very public professions,"
Kidman recently praised Urban for "grounding" her and keeping her down to earth.