Information About Segments of Business Reconciliation of Assets from Segment to Consolidated (Details) - USD ($) $ in Millions		Dec. 31, 2020	Dec. 31, 2019
Segment Reporting, Asset Reconciling Item
Assets		$ 22,815.2	$ 21,076.3
General Insurance Group [Member]
Segment Reporting, Asset Reconciling Item
Assets		19,226.1	17,870.0
Title Insurance Group [Member]
Segment Reporting, Asset Reconciling Item
Assets		1,920.9	1,695.0
RFIG Run-off Business [Member]
Segment Reporting, Asset Reconciling Item
Assets		582.9	615.1
Total of major segments [Member]
Segment Reporting, Asset Reconciling Item
Assets		21,730.0	20,180.2
All Other Segments [Member]
Segment Reporting, Asset Reconciling Item
Assets	[1]	1,318.2	1,095.4
Business Intersegment, Eliminations [Member]
Segment Reporting, Asset Reconciling Item
Assets		$ (233.0)	$ (199.3)

[1] Includes amounts for a small life and accident insurance business as well as those of the parent holding company and its internal corporate services subsidiaries