Recent Accounting Pronouncements (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2012	Dec. 31, 2012
Previous Accounting Guidance [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Policy acquisition costs deferred	$ 126.6
Deferred policy acquisition cost, amortization expense	119.3
Accounting Standards Update 2010-26 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Costs expected to be recognized in income, effect of adoption		43
Policy acquisition costs deferred	99.0
Deferred policy acquisition cost, amortization expense	$ 112.0