Schedule 2 - Parent Company Financial Statements - Statements of Comprehensive Income (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Condensed Financial Statements, Captions [Line Items]
Net Income	$ 1.9	$ 55.6	$ 2.3	$ 43.6	$ 24.3	$ 2.0	$ (3.3)	$ 51.5	$ 103.4	$ 74.5	$ 177.9
Unrealized Holding Gains (Losses) Arising During the Year:
Securities Held by Parent									157.9	232.1	195.8
Reclassification Adjustment for Amounts Included in Net Income:
Securities Held by Parent									(61.2)	(30.9)	(18.8)
Unrealized Holding Gains (Losses)									96.7	201.2	177.0
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)
Foreign Currency Translation Adjustments									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
Other Comprehensive Income Before Income Taxes									85.1	156.4	152.7
Income Tax Benefit (Expense):
Securities Held by Parent									(55.9)	(82.5)	(69.2)
Securities Held by Parent									21.5	10.9	6.6
Unrealized Holding Gains and Losses									(34.4)	(71.6)	(62.6)
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
Foreign Currency Translation Adjustments									(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 of Subsidiary									0	0	(1.0)
Other Comprehensive Income Tax Benefit (Expense)									(30.4)	(55.8)	(54.1)
Other Comprehensive Income									54.7	100.6	98.6
Parent Company [Member]
Condensed Financial Statements, Captions [Line Items]
Net Income									103.4	74.5	177.9
Unrealized Holding Gains (Losses) Arising During the Year:
Securities Held by Subsidiaries									157.9	231.5	195.7
Securities Held by Parent									0	0.6	0.1
Reclassification Adjustment for Amounts Included in Net Income:
Securities Held by Subsidiaries									61.2	30.2	18.8
Securities Held by Parent									0	(0.7)	0
Unrealized Holding Gains (Losses)									96.7	201.2	177.0
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)
Foreign Currency Translation Adjustments									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
Other Comprehensive Income Before Income Taxes									85.1	156.4	152.7
Income Tax Benefit (Expense):
Securities Held by Subsidiaries									(55.9)	(82.3)	(69.2)
Securities Held by Parent									0	(0.2)	0
Securities Held by Subsidiaries									21.5	10.7	6.6
Securities Held by Parent									0	0.2	0
Unrealized Holding Gains and Losses									(34.4)	(71.6)	(62.6)
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
Foreign Currency Translation Adjustments									(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 of Subsidiary									0	0	(1.0)
Other Comprehensive Income Tax Benefit (Expense)									(30.4)	(55.8)	(54.1)
Other Comprehensive Income									54.7	100.6	98.6
Total Comprehensive Income									$ 158.1	$ 175.1	$ 276.5