Schedule of Other Comprehensive Income (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012	Dec. 31, 2011
Changes in Components of Accumulated Other Comprehensive Income [Line Items]
Stockholders' Equity Attributable to Parent	$ 8,557.8	$ 8,179.9	$ 8,612.6
Other Comprehensive Income (Loss), Net of Tax	(142.3)	(6.4)
Total Reclassification Adjustments from AOCI to Net Income, Net of Tax	0.4
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax [Abstract]
Reclassification Adjustment for Sale of Securities Included in Net Income, Net of Tax	(7.8)
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	(278.5)	(197.2)
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax [Abstract]
Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain from Cash Flow Hedges, Effect Net of Tax	399.6		401.6
Other Comprehensive Income (Loss), Unrealized (Loss) on Derivatives Arising During Period, Net of Tax	(1.2)
Cash Flow Hedge Gain Reclassified to Earnings, Net of Tax	(0.8)
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	(2.0)	(10.7)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax [Abstract]
Accumulated Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Net of Tax	(142.5)		(72.6)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Loss Arising During Period, Net of Tax	(69.9)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Reclassification Adjustment Realized upon Sale or Liquidation, Net of Tax	0
Change in Foreign Currency Translation Adjustment	(69.9)	28.2
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax [Abstract]
Accumulated Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net of Tax	(563.8)		(574.5)
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net Unamortized Gain Arising During Period, Net of Tax	1.7
Reclassification Adjustment on Pension and Other Postretirement Benefit Plans, Net Loss Recognized in Net Periodic Benefit Cost, Net of Tax	9.0
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax	10.7
Accumulated Other Comprehensive Income [Member]
Changes in Components of Accumulated Other Comprehensive Income [Line Items]
Stockholders' Equity Attributable to Parent	485.7	455.4	628.0	461.8
Other Comprehensive Income (Loss), Net of Tax	(142.3)	(6.4)
Before Reclassification Adjustment [Member]
Changes in Components of Accumulated Other Comprehensive Income [Line Items]
Other Comprehensive Income (Loss), Net of Tax	(142.7)
Includes Unrealized Adjustment for Deferred Policy Acquisition Costs and Reserves for Future Policy and Contract Benefits [Member]
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax [Abstract]
Accumulated Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	792.4		873.5
Other Comprehensive Income (Loss), Unrealized Holding (Loss) on Securities Arising During Period, Net of Tax	(73.3)
Reclassification Adjustment for Sale of Securities Included in Net Income, Net of Tax	(7.8)
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	$ (81.1)