They intended to demolish it and replace it with a modern hotel, but World War I material shortages delayed the work.

The hotel operated successfully until the Great Depression, when banks foreclosed and the Book brothers lost control in 1931.

On May 2, 1939, a meeting took place in the hotel lobby between New York Yankees first baseman Lou Gehrig and team manager Joe McCarthy in which Gehrig told McCarthy to leave him out of the starting line-up from that day's game against the Detroit Tigers, ending his 2,130 consecutive games streak.

By that point, multiple guestroom floors of the aging hotel had been entirely closed off and mothballed, and only 768 of its 947 rooms were considered "saleable."

However, those plans were quickly dashed, as proposed construction costs soared, and Detroit's economic situation continued to deteriorate.

After the sale, the hotel's retail tenants, who had planned to stay through the renovation, moved out and the building was shuttered.

Time passed and the unmaintained property decayed, a it fell victim to the elements, vandalism, and urban scavengers.

Work started shortly after the announcement, but came to a halt in November, when construction crews discovered more damage than anticipated.

A new renovation plan, through the Cleveland-based Ferchill Group, was announced in June 2006, with the Book-Cadillac to become a Westin Hotel and Residences.

[8] Architect Louis Kamper designed the hotel in the Renaissance Revival style at the corner of Washington Boulevard and Michigan Avenue.

Among its notable features are the sculptures of notable figures from Detroit's history—General Anthony Wayne, Antoine Laumet de La Mothe, sieur de Cadillac, Chief Pontiac, and Robert Navarre along the ornate Michigan Avenue façade and copper-covered roof elements.

When the north penthouse was reconstructed, it was built 18 ft (5.5 m) shorter to make the ziggurats the highest points of the building.

[3] The building sits atop three basements, which contain some inoperable mechanical equipment too large to remove during renovation.