Accumulated Other Comprehensive Income (Loss) - Changes in Accumulated Other Comprehensive Income (Loss) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014
Accumulated Other Comprehensive Income Loss [Line Items]
Accumulated Other Comprehensive Income (Loss) Net Of Tax, Beginning Balance	$ 108.1	[1]	$ 147.8
Other comprehensive (loss) income before reclassifications	(24.6)		1.1
Amounts reclassified from accumulated other comprehensive income (loss)	2.6		0
Other comprehensive (loss) income, net of tax	(22.0)		1.1
Accumulated Other Comprehensive Income (Loss) Net Of Tax, Ending Balance	86.1		148.9
Foreign Currency Translation Adjustments
Accumulated Other Comprehensive Income Loss [Line Items]
Accumulated Other Comprehensive Income (Loss) Net Of Tax, Beginning Balance	(15.6)		(11.5)
Other comprehensive (loss) income before reclassifications	(3.1)		(0.2)
Amounts reclassified from accumulated other comprehensive income (loss)	0		0
Other comprehensive (loss) income, net of tax	(3.1)		(0.2)
Accumulated Other Comprehensive Income (Loss) Net Of Tax, Ending Balance	(18.7)		(11.7)
Unrealized Holding Gains on Securities
Accumulated Other Comprehensive Income Loss [Line Items]
Accumulated Other Comprehensive Income (Loss) Net Of Tax, Beginning Balance	130.7		163.9
Other comprehensive (loss) income before reclassifications	(21.5)		1.3
Amounts reclassified from accumulated other comprehensive income (loss)	2.6		0
Other comprehensive (loss) income, net of tax	(18.9)		1.3
Accumulated Other Comprehensive Income (Loss) Net Of Tax, Ending Balance	111.8		165.2
Defined Benefit Pension Plans
Accumulated Other Comprehensive Income Loss [Line Items]
Accumulated Other Comprehensive Income (Loss) Net Of Tax, Beginning Balance	(7.0)		(4.6)
Other comprehensive (loss) income before reclassifications	0		0
Amounts reclassified from accumulated other comprehensive income (loss)	0		0
Other comprehensive (loss) income, net of tax	0		0
Accumulated Other Comprehensive Income (Loss) Net Of Tax, Ending Balance	$ (7.0)		$ (4.6)

[1] Derived from audited consolidated financial statements.