No domestic insurer may engage, directly or indirectly, in any business other than insurance and business reasonably incidental to its insurance business, except as specifically authorized by s. 611.26 (4), 611.26 (4) as incorporated by s. 614.24 (1), or s. 613.26 or any other provision of chs. 600 to 646;except that a domestic insurer not restricted under s. 620.03 may engage directly in any acti