details wrap normal unless they contain newlines, https://github.com/microsoft/vscode/issues/99370

src/vs/editor/contrib/suggest/media/suggest.css

@@ -354,6 +354,11 @@
 	padding: 4px 0 12px 5px;
 }
 
+.monaco-editor .suggest-details>.monaco-scrollable-element>.body>.header>.type.auto-wrap {
+	white-space: normal;
+}
+
+
 .monaco-editor .suggest-details>.monaco-scrollable-element>.body>.docs {
 	margin: 0;
 	padding: 4px 5px;

src/vs/editor/contrib/suggest/suggestWidgetDetails.ts

@@ -142,12 +142,16 @@ export class SuggestDetailsWidget {
 
 		this.domNode.classList.remove('no-docs', 'no-type');
 
+		let detailsLines = 0;
 		// --- details
+
 		if (detail) {
 			const cappedDetail = detail.length > 100000 ? `${detail.substr(0, 100000)}…` : detail;
 			this._type.textContent = cappedDetail;
 			this._type.title = cappedDetail;
 			dom.show(this._type);
+			detailsLines = count(cappedDetail, '\n');
+			this._type.classList.toggle('auto-wrap', detailsLines === 0);
 		} else {
 			dom.clearNode(this._type);
 			this._type.title = '';
@@ -186,7 +190,7 @@ export class SuggestDetailsWidget {
 
 		let heightInLines = 0;
 		if (detail) {
-			heightInLines += 2 + count(detail, '\n');
+			heightInLines += 2 + detailsLines;
 		}
 		if (documentation) {
 			heightInLines += 5;