Summary of Significant Accounting Policies (Recently Adopted Changes in Accounting Principles) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012	Jan. 02, 2012 Accounting Standards Update 2010-26 [Member]
New Accounting Pronouncement, Early Adoption [Line Items]
Deferred acquisition costs	$ 188.2	$ 195.3	$ 5.6