Other Comprehensive Income And Accumulated Other Comprehensive Income (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Other Comprehensive Income (Loss) Before Income Taxes:
Unrealized Holding Gains (Losses) Arising During the Period Before Reclassification Adjustment	$ 157.9	$ 232.1	$ 195.8
Reclassification Adjustment for Amounts Included in Net Income	61.2	30.9	18.8
Unrealized Holding Gains (Losses)	96.7	201.2	177.0
Foreign Currency Translation Adjustments Arising During the Period Before Reclassification Adjustment	1.6	0.4	(2.6)
Reclassification Adjustment for Amounts Included in Net Income	0	0	(2.1)
Foreign Currency Translation Adjustments	1.6	0.4	(0.5)
Equity in Other Comprehensive Income of Former Investee, Before Income Taxes	0	0	2.9
Unrecognized Postretirement Benefit Costs Arising During the Year	(29.4)	(53.9)	(27.9)
Amortization of Unrecognized Postretirement Benefit Costs	16.2	8.7	1.2
Net Unrecognized Postretirement Benefit Costs	13.2	45.2	26.7
Other Comprehensive Income Before Income Taxes	85.1	156.4	152.7
Income Tax Benefit (Expense):
Unrealized Holding Gains and Losses Arising During the Period Before Reclassification Adjustment	(55.9)	(82.5)	(69.2)
Reclassification Adjustment for Amounts Included in Net Income	21.5	10.9	6.6
Unrealized Holding Gains and Losses	(34.4)	(71.6)	(62.6)
Foreign Currency Translation Adjustments Arising During the Period Before Reclassification Adjustment	(0.6)	(0.1)	1.0
Reclassification Adjustment for Amounts Included in Net Income	0	0	(0.8)
Foreign Currency Translation Adjustment	(0.6)	(0.1)	0.2
Equity in Other Comprehensive (Income) Loss of Former Investee	0	0	(1.0)
Unrecognized Postretirement Benefit Costs Arising During the Year	10.3	19.0	9.8
Amortization of Unrecognized Postretirement Benefit Costs	(5.7)	(3.1)	(0.5)
Net Unrecognized Postretirement Benefit Costs	4.6	15.9	9.3
Other Comprehensive Income Tax Benefit (Expense)	$ (30.4)	$ (55.8)	$ (54.1)