CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Comprehensive Income (Loss) [Line Items]
Net income	$ 55.9	$ 36.7	$ 151.2
Available-for-sale securities and derivative instruments:
Net appreciation during the period	151.3	65.1	97.8
Portion of other-than-temporary impairment losses transferred from (to) other comprehensive income	12.2	10.5	6.9
Benefit (provision) for deferred income taxes	(46.2)	14.8	5.9
Other comprehensive income	117.3	90.4	110.6
Pension and postretirement benefits:
Net actuarial loss arising in the period	(24.9)	(16.0)	(13.9)
Amortization recognized as net periodic benefit costs:
Net actuarial loss	13.0	15.4	17.2
Prior service cost	(3.7)	(5.2)	(5.8)
Transition asset			(1.6)
Total amortization recognized as net periodic pension and postretirement cost	9.3	10.2	9.8
Decrease from pension and postretirement benefit costs	(15.6)	(5.8)	(4.1)
Benefit for deferred income taxes	5.8	0.6	1.4
Total pension and postretirement benefits	(9.8)	(5.2)	(2.7)
Cumulative foreign currency translation adjustment:
Amount recognized as cumulative foreign currency translation during the period	12.2	(17.7)
Benefit (provision) for deferred income taxes	(4.3)	6.2
Total cumulative foreign currency translation adjustment	7.9	(11.5)
Other comprehensive income	115.4	73.7	107.9
Comprehensive income	$ 171.3	$ 110.4	$ 259.1