Changes in Other Comprehensive Income (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Accumulated Other Comprehensive Income (Loss) [Line Items]
Unrealized gains arising during period	$ 25.0	$ 70.0
Amount of realized gains from sales and other	8.8	4.7
Portion of other-than-temporary impairment losses recognized in earnings	(0.5)	(2.9)
Net unrealized gains	16.7	68.2
Amortization of net actuarial loss and prior service cost recognized as net periodic benefit cost	2.9	2.3
Foreign currency translation recognized during the period	(15.4)	14.3
Other comprehensive income (loss)	4.2	84.8
Unrealized gains arising during period	(8.8)	(20.9)
Amount of realized gains from sales and other	2.3	2.7
Portion of other-than-temporary impairment losses recognized in earnings	0.2	0.7
Net unrealized gains	(11.3)	(24.3)
Amortization of net actuarial loss and prior service cost recognized as net periodic benefit cost	(1.0)	(0.8)
Foreign currency translation recognized during the period	5.4	(5.0)
Other comprehensive income (loss)	(6.9)	(30.1)
Unrealized gains arising during period	16.2	49.1
Amount of realized gains from sales and other	11.1	7.4
Portion of other-than-temporary impairment losses recognized in earnings	(0.3)	(2.2)
Net unrealized gains	5.4	43.9
Amortization of net actuarial loss and prior service cost recognized as net periodic benefit cost	1.9	1.5
Foreign currency translation recognized during the period	(10.0)	9.3
Other comprehensive income (loss)	$ (2.7)	$ 54.7