CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Parenthetical) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Statement of Comprehensive Income [Abstract]
Change in Net Unrealized Gain on Securities Before Adjustment, Tax Expense (Benefit)	$ 725.8	$ (1,102.8)	$ 467.7
Change in Adjustment to Deferred Acquisition Costs and Reserves for Future Policy and Contract Benefits, Net of Reinsurance, Tax Expense (Benefit)	(665.1)	743.3	(325.6)
Change in Net Gain on Cash Flow Hedges, Tax Benefit	2.0	1.3	4.3
Change in Unrecognized Pension and Postretirement Benefit Costs, Tax Expense (Benefit)	$ (92.4)	$ 185.2	$ (68.0)