Fair Value Measurements (Details 5) (Nonrecurring Fair Value Measurements, Fair value hierarchy Level 3, USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Mortgage loans
Assets and liabilities measured at fair value on a nonrecurring basis
Fair value of assets measured on nonrecurring basis	$ 78.0	$ 172.7	$ 78.0	$ 172.7
Net (gain) loss due to change in fair value of assets measured on nonrecurring basis	8.9	3.4	17.7	11.2
Mortgage loans | Minimum
Assets and liabilities measured at fair value on a nonrecurring basis
Discount rate (as a percent)			9.50%	8.00%
Terminal capitalization rate (as a percent)			7.50%	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)			7.00%	8.00%
Mortgage servicing rights
Assets and liabilities measured at fair value on a nonrecurring basis
Fair value of assets measured on nonrecurring basis	7.9	5.9	7.9	5.9
Net (gain) loss due to change in fair value of assets measured on nonrecurring basis	$ (1.1)	$ 0.1	$ (1.3)	$ 0
Mortgage servicing rights | Input
Assets and liabilities measured at fair value on a nonrecurring basis
Discount rate (as a percent)			3.80%	3.10%