Income Taxes - Tax Credit and Loss Carryforwards (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Operating Loss Carryforwards [Line Items]
Tax capital loss/credit carryforward	$ 274.3	$ 279.1
State
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	2,412.8	2,376.0
Federal
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	2,953.4	2,871.5
Alternative minimum tax [Member]
Operating Loss Carryforwards [Line Items]
Tax capital loss/credit carryforward	209.5
Capital loss carryforwards | Federal
Operating Loss Carryforwards [Line Items]
Tax capital loss/credit carryforward	$ 0	$ 88.3