Other Comprehensive Income And Accumulated Other Comprehensive Income (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Other Comprehensive Income (Loss) Before Income Taxes:
Unrealized Holding Gains (Losses) Arising During the Period Before Reclassification Adjustment	$ 259.7	$ (324.9)	$ 157.9
Reclassification Adjustment for Amounts Included in Net Income	(25.1)	(37.9)	(61.2)
Unrealized Holding Gains (Losses)	234.6	(362.8)	96.7
Foreign Currency Translation Adjustments Arising During the Period Before Reclassification Adjustment	(1.0)	0.2	1.6
Reclassification Adjustment for Amounts Included in Net Income	0	0	0
Foreign Currency Translation Adjustments	(1.0)	0.2	1.6
Unrecognized Postretirement Benefit Costs Arising During the Year	(106.4)	61.6	(29.4)
Amortization of Net Unrecognized Postretirement Benefit Costs	7.9	25.0	16.2
Net Unrecognized Postretirement Benefit Costs	(98.5)	86.6	(13.2)
Other Comprehensive Income (Loss) Before Income Taxes	135.1	(276.0)	85.1
Income Tax Benefit (Expense):
Unrealized Holding Gains and Losses Arising During the Year Before Reclassification Adjustment	(91.6)	115.9	(55.9)
Reclassification Adjustment for Amounts Included in Net Income	8.8	13.2	21.5
Unrealized Holding Gains and Losses	(82.8)	129.1	(34.4)
Foreign Currency Translation Adjustments Arising During the Period Before Reclassification Adjustment	0.4	(0.1)	(0.6)
Reclassification Adjustment for Amounts Included in Net Income	0	0	0
Foreign Currency Translation Adjustment	0.4	(0.1)	(0.6)
Unrecognized Postretirement Benefit Costs Arising During the Year	37.5	(21.6)	10.3
Amortization of Unrecognized Postretirement Benefit Costs	(2.8)	(8.8)	(5.7)
Net Unrecognized Postretirement Benefit Costs	34.7	(30.4)	4.6
Other Comprehensive Income Tax Benefit (Expense)	$ (47.7)	$ 98.6	$ (30.4)