Identifiable Assets for Business Segments and Discontinued Operations (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Segment Reporting Information [Line Items]
Discontinued operations	$ 120.6	$ 130.5
Total assets	13,442.1	13,484.9
U.S. Companies
Segment Reporting Information [Line Items]
Identifiable assets	8,908.5	8,909.6
Chaucer
Segment Reporting Information [Line Items]
Identifiable assets	$ 4,413.0	$ 4,444.8