Investment Securities (Cost and Amortized Cost Maturity Schedule) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013
Trading Securities by Maturity Cost or Amortized Cost
Cost or amortized cost	$ 5,337.6
Trading Securities by Maturity, Fair Value
Trading Securities	5,347.3
Fixed Maturities and Convertible Fixed Maturities Excluding A B S M B S and Preferred Stock
Trading Securities by Maturity Cost or Amortized Cost
Due in one year or less	491.2
Due after one year through five years	2,376.7
Due after five years through ten years	321.0
Due after ten years	41.5
Trading Securities by Maturity, Fair Value
Due in one year or less	490.7
Due after one year through five years	2,389.3
Due after five years through ten years	322.2
Due after ten years	45.8
Mortgage-backed and asset-backed securities
Trading Securities by Maturity Cost or Amortized Cost
Trading Securities, Maturities without Single Maturity Date, Amortized Cost	2,027.3
Trading Securities by Maturity, Fair Value
Trading Securities, Maturities without Single Maturity Date, Carrying Value	2,014.5
Preferred stocks
Trading Securities by Maturity Cost or Amortized Cost
Trading Securities, Maturities without Single Maturity Date, Amortized Cost	79.9
Trading Securities by Maturity, Fair Value
Trading Securities, Maturities without Single Maturity Date, Carrying Value	$ 84.8