Consolidated Statements of Comprehensive Income (Loss) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
Consolidated Statements of Comprehensive Income (Loss)
Net income	$ 154.8	$ 197.2	$ 20.6
Available-for-sale securities:
Net appreciation (depreciation) during the period	97.8	423.1	(284.9)
Portion of other-than-temporary impairment losses transferred from (to) other comprehensive income	6.9	(7.3)
Benefit for deferred federal income taxes	5.9	1.3	2.9
Total available-for-sale securities	110.6	417.1	(282.0)
Derivative instruments:
Net appreciation during the period			0.6
Provision for deferred federal income taxes			(0.2)
Total derivative instruments			0.4
Other Comprehensive income (loss)	110.6	417.1	(281.6)
Pension and postretirement benefits:
Net actuarial (loss) gain	(13.9)	21.5	(126.9)
Prior service cost		4.5	3.1
Total amounts arising in the period	(13.9)	26.0	(123.8)
Amortization recognized as net periodic benefit costs:
Net actuarial loss	17.2	27.2	3.0
Prior service cost	(5.8)	(5.8)	(4.9)
Transition asset	(1.6)	(1.6)	(1.7)
Total amortization recognized as net periodic pension and postretirement cost (benefit)	9.8	19.8	(3.6)
(Decrease) increase in pension and postretirement benefit costs	(4.1)	45.8	(127.4)
Benefit (provision) for deferred federal income taxes	1.4	(16.0)	44.6
Total pension and postretirement benefits	(2.7)	29.8	(82.8)
Other comprehensive income (loss)	107.9	446.9	(364.4)
Comprehensive income (loss)	$ 262.7	$ 644.1	$ (343.8)