Fair Value Measurements (Details 5) (Nonrecurring Fair Value Measurements, Fair value hierarchy Level 3, USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Mortgage loans
Assets and liabilities measured at fair value on a nonrecurring basis
Fair value of assets measured on nonrecurring basis	$ 23.4	$ 64.2
Net (gain) loss due to change in fair value of assets measured on nonrecurring basis	(0.4)	8.8
Mortgage loans | Minimum
Assets and liabilities measured at fair value on a nonrecurring basis
Discount rate (as a percent)		10.30%
Terminal capitalization rate (as a percent)	7.30%	8.00%
Average market rent growth rate (as a percent)	3.00%	1.00%
Mortgage loans | Maximum
Assets and liabilities measured at fair value on a nonrecurring basis
Discount rate (as a percent)		20.00%
Terminal capitalization rate (as a percent)	9.00%	10.50%
Average market rent growth rate (as a percent)	10.90%	5.00%
Mortgage loans | Input
Assets and liabilities measured at fair value on a nonrecurring basis
Discount rate (as a percent)	11.00%
Mortgage servicing rights
Assets and liabilities measured at fair value on a nonrecurring basis
Fair value of assets measured on nonrecurring basis		6.9
Net (gain) loss due to change in fair value of assets measured on nonrecurring basis		$ (0.2)
Mortgage servicing rights | Input
Assets and liabilities measured at fair value on a nonrecurring basis
Discount rate (as a percent)		3.20%