Insouciance is a state of calm; the quality or state of being untroubled and carefree.
[Freddie] smiled at Jurgis confidingly, and then started talking again, with his blissful insouciance. This time he talked for ten minutes at a stretch, and in the course of the speech he told Jurgis all of his family history.
From Upton Sinclair's The Jungle.
