Business, Basis of Presentation and Significant Accounting Policies (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended												3 Months Ended	9 Months Ended								3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011	Dec. 31, 2010	Sep. 30, 2012 Retained Earnings (Deficit)	Dec. 31, 2011 Retained Earnings (Deficit)	Sep. 30, 2011 Retained Earnings (Deficit)	Dec. 31, 2010 Retained Earnings (Deficit)	Sep. 30, 2012 Accumulated Other Comprehensive Income (Loss)	Dec. 31, 2011 Accumulated Other Comprehensive Income (Loss)	Sep. 30, 2011 Accumulated Other Comprehensive Income (Loss)	Dec. 31, 2010 Accumulated Other Comprehensive Income (Loss)	Sep. 30, 2011 Cumulative effect of changes in accounting	Sep. 30, 2011 Cumulative effect of changes in accounting	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	Sep. 30, 2012 Accounting change to employee benefit plans to recognize actuarial gains and losses immediately in net income	Sep. 30, 2011 Accounting change to employee benefit plans to recognize actuarial gains and losses immediately in net income	Sep. 30, 2012 Accounting change to employee benefit plans to recognize actuarial gains and losses immediately in net income	Sep. 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)
Retained Earnings Adjustments [Line Items]
Fee income	$ 167.0	$ 152.5	$ 478.8	$ 468.3											$ 0.5	$ (2.4)
Other net realized capital gains (losses)	(21.1)	(125.8)	108.0	(52.3)											(148.8)	(151.9)
Other income	1.0	1.2	3.8	14.1											(2.4)	(2.8)
Interest credited and other benefits to contract owners	189.3	191.8	577.0	551.1											(150.7)	(157.1)
Effect of change in accounting, adoption of new pronouncement																												7.2	21.3	7.2	21.3
Change in net income, due to change in accounting principal																								0.8	0.8	2.5	2.0
Stockholders' Equity Attributable to Parent	4,242.1	3,838.7	4,242.1	3,838.7	3,976.3	3,092.0	(1,031.8)	(1,307.0)	(1,346.5)	(1,627.3)	1,054.2	747.5	654.9	390.5			(366.3)	(431.0)	64.7	3,458.3	(1,175.0)	304.5
Effect of change in accounting, adoption of new pronouncement, taxes																							$ 232.1