Fair Value Measurements (Details 5) (Nonrecurring Fair Value Measurements, Fair value hierarchy Level 3, USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Mortgage loans
Assets and liabilities measured at fair value on a nonrecurring basis
Fair value of assets measured on nonrecurring basis	$ 153.1	$ 173.8	$ 206.0
Net (gain) loss due to change in fair value of assets measured on nonrecurring basis	27.5	12.3	27.7
Mortgage loans | Minimum
Assets and liabilities measured at fair value on a nonrecurring basis
Discount rate (as a percent)	8.00%	8.00%
Terminal capitalization rate (as a percent)	7.30%	6.30%
Average market rent growth rate (as a percent)	1.00%	3.00%
Mortgage loans | Maximum
Assets and liabilities measured at fair value on a nonrecurring basis
Discount rate (as a percent)	20.00%	20.00%
Terminal capitalization rate (as a percent)	10.50%	10.50%
Average market rent growth rate (as a percent)	10.90%	8.00%
Mortgage servicing rights
Assets and liabilities measured at fair value on a nonrecurring basis
Fair value of assets measured on nonrecurring basis	7.3	7.0	4.4
Net (gain) loss due to change in fair value of assets measured on nonrecurring basis	(1.3)	(0.4)	1.1
Mortgage servicing rights | Input
Assets and liabilities measured at fair value on a nonrecurring basis
Discount rate (as a percent)	4.30%	3.10%
Real estate
Assets and liabilities measured at fair value on a nonrecurring basis
Fair value of assets measured on nonrecurring basis		5.0	3.9
Net (gain) loss due to change in fair value of assets measured on nonrecurring basis		$ 0.1	$ 0.6