CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Parenthetical) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Change in Net Unrealized Gains and Losses on Securities Not Other-Than-Temporarily Impaired, tax benefit	$ 110.2	$ 40.7
Change in Net Unrealized Gains and Losses on Securities Other-Than-Temporarily Impaired, tax benefit	0	1.1
Total Change in Net Unrealized Gain on Securities Before Reclassification Adjustment, tax benefit	110.2	41.8
Reclassification Adjustment for Net Realized Investment (Gain) Loss, tax expense	0.3	0.5
Change in Net Gain on Cash Flow Hedges, tax benefit	5.9	5.4
Change in Adjustment to Reserves for Future Policy and Contract Benefits Net of Reinsurance and Other, tax expense	97.2	59.8
Change in Unrecognized Pension and Postretirement Benefit Costs, tax expense	$ 3.0	$ 1.6