Identifiable Assets for Business Segments and Discontinued Operations (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Segment Reporting Information [Line Items]
Discontinued operations	$ 130.5	$ 121.2
Total assets	13,484.9	12,598.6
U.S. Companies
Segment Reporting Information [Line Items]
Identifiable assets	8,909.6	8,471.6
Chaucer
Segment Reporting Information [Line Items]
Identifiable assets	$ 4,444.8	$ 4,005.8