Summary of Significant Accounting Policies (Recently Adopted in Accounting Principles) (Details) (USD $) In Millions, unless otherwise specified				12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Jan. 31, 2010 Cumulative-Effect Adjustment, Deconsolidation of Variable Interest Entity Variable Interest Entity, Not Primary Beneficiary	Dec. 31, 2012 Accounting Standards Update 2010-26
Variable Interest Entity [Line Items]
Change in accounting principle from new accounting pronouncement			$ 0.4
Deferred acquisition costs	195.3	187.0
Deferred policy acquisition costs, amortization expense				$ 5.6