Business, Basis of Presentation and Significant Accounting Policies (Details) (USD $) In Millions, unless otherwise specified													3 Months Ended		6 Months Ended													3 Months Ended	6 Months Ended	3 Months Ended	6 Months Ended	3 Months Ended	6 Months Ended
	Jun. 30, 2012	Dec. 31, 2011	Jun. 30, 2011	Dec. 31, 2010	Jun. 30, 2012 Retained Earnings (Deficit)	Dec. 31, 2011 Retained Earnings (Deficit)	Jun. 30, 2011 Retained Earnings (Deficit)	Dec. 31, 2010 Retained Earnings (Deficit)	Jun. 30, 2012 Accumulated Other Comprehensive Income (Loss)	Dec. 31, 2011 Accumulated Other Comprehensive Income (Loss)	Jun. 30, 2011 Accumulated Other Comprehensive Income (Loss)	Dec. 31, 2010 Accumulated Other Comprehensive Income (Loss)	Jun. 30, 2012 Accounting change to employee benefit plans to recognize actuarial gains and losses immediately in net income	Jun. 30, 2011 Accounting change to employee benefit plans to recognize actuarial gains and losses immediately in net income	Jun. 30, 2012 Accounting change to employee benefit plans to recognize actuarial gains and losses immediately in net income	Jun. 30, 2011 Accounting change to employee benefit plans to recognize actuarial gains and losses immediately in net income	Dec. 31, 2011 Accounting change to employee benefit plans to recognize actuarial gains and losses immediately in net income Retained Earnings (Deficit)	Jan. 02, 2011 Accounting change to employee benefit plans to recognize actuarial gains and losses immediately in net income Retained Earnings (Deficit)	Dec. 31, 2011 Accounting change to employee benefit plans to recognize actuarial gains and losses immediately in net income Accumulated Other Comprehensive Income (Loss)	Jan. 02, 2011 Accounting change to employee benefit plans to recognize actuarial gains and losses immediately in net income Accumulated Other Comprehensive Income (Loss)	Dec. 31, 2010 Cumulative effect of changes in accounting Deferred policy acquisition costs	Dec. 31, 2010 Cumulative effect of changes in accounting Deferred policy acquisition costs Retained Earnings (Deficit)	Dec. 31, 2010 Cumulative effect of changes in accounting Deferred policy acquisition costs Accumulated Other Comprehensive Income (Loss)	Dec. 31, 2010 As previously filed	Dec. 31, 2010 As previously filed Retained Earnings (Deficit)	Dec. 31, 2010 As previously filed Accumulated Other Comprehensive Income (Loss)	Jan. 02, 2012 As previously filed Deferred policy acquisition costs	Jun. 30, 2011 Interest Credited and Other Benefits to Contract Owners [Member]	Jun. 30, 2011 Interest Credited and Other Benefits to Contract Owners [Member]	Jun. 30, 2011 Fee Income [Member]	Jun. 30, 2011 Fee Income [Member]	Jun. 30, 2011 Other Net Realized Capital Gains (Losses) [Member]	Jun. 30, 2011 Other Net Realized Capital Gains (Losses) [Member]
Retained Earnings Adjustments [Line Items]
Stockholders' Equity Attributable to Parent	$ 3,987.0	$ 3,976.3	$ 3,575.2	$ 3,092.1	$ (1,125.1)	$ (1,307.0)	$ (1,423.3)	$ (1,627.3)	$ 892.1	$ 747.5	$ 468.2	$ 390.6									$ (366.2)	$ (431.0)	$ 64.8	$ 3,458.3	$ (1,175.0)	$ 304.5
Prior priod reclassification adjustment																												7.9	(5.7)	(1.3)	2.6	(6.6)	3.1
Change in net income, due to change in accounting principal													0.9	1.7	0.5	1.2
Effect of change in accounting, adoption of new pronouncement																	7.2	21.3	7.2	21.3
Effect of change in accounting, adoption of new pronouncement, taxes																											$ 232.1