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, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Mortgage loans
Assets and liabilities measured at fair value on a nonrecurring basis
Fair value of assets measured on nonrecurring basis	$ 172.7	$ 97.4	$ 172.7	$ 97.4
Net (gain) loss due to change in fair value of assets measured on nonrecurring basis	3.4	14.8	11.2	14.0
Mortgage loans | Minimum
Assets and liabilities measured at fair value on a nonrecurring basis
Discount rate (as a percent)			8.00%
Terminal capitalization rate (as a percent)			6.30%
Average market rent growth rate (as a percent)			3.00%
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)			10.50%
Average market rent growth rate (as a percent)			8.00%
Mortgage servicing rights
Assets and liabilities measured at fair value on a nonrecurring basis
Fair value of assets measured on nonrecurring basis	5.9	1.0	5.9	1.0
Net (gain) loss due to change in fair value of assets measured on nonrecurring basis	$ 0.1	$ 0.1	$ 0	$ 0
Mortgage servicing rights | Input
Assets and liabilities measured at fair value on a nonrecurring basis
Discount rate (as a percent)			3.10%