Identifiable Assets for Business Segments and Discontinued Operations (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Segment Reporting Information [Line Items]
Discontinued operations	$ 122.2	$ 121.2
Total assets	13,118.7	12,598.6
U.S. Companies
Segment Reporting Information [Line Items]
Identifiable assets	8,609.5	8,471.6
Chaucer
Segment Reporting Information [Line Items]
Identifiable assets	$ 4,387.0	$ 4,005.8