Income Tax (Benefit)(Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income Tax [Abstract]
Net Income	$ 347.1	$ 355.1	$ 49.1
Additional Paid in Capital [Abstract]
Stock-Based Compensation	(0.8)	3.5	(3.3)
Other Comprehensive Income (Loss), Tax [Abstract]
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Tax	(1,102.8)	467.7	798.3
Change in Adjustment to Reserves for Future Policy and Contract Benefits Net of Reinsurance and Other tax expense benefit	(743.3)	325.6	701.5
Change in Net Gain on Cash Flow Hedges	(1.3)	(4.3)	25.2
Change in Unrecognized Pension and Postretirement Benefit Costs	185.2	(68.0)	(67.4)
Total	$ 170.7	$ 428.4	$ 100.4