Fair Value Measurements (Details 5) (Nonrecurring Fair Value Measurements, Fair value hierarchy Level 3, USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Mortgage loans
Assets and liabilities measured at fair value on a nonrecurring basis
Fair value of assets measured on nonrecurring basis	$ 172.5	$ 104.4	$ 172.5	$ 104.4
Net (gain) loss due to change in fair value of assets measured on nonrecurring basis	3.1	2.1	14.4	16.1
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	5.6	4.9	5.6	4.9
Net (gain) loss due to change in fair value of assets measured on nonrecurring basis	0.2	0.9	0.3	1.0
Mortgage servicing rights | Input
Assets and liabilities measured at fair value on a nonrecurring basis
Discount rate (as a percent)			3.00%
Real estate
Assets and liabilities measured at fair value on a nonrecurring basis
Fair value of assets measured on nonrecurring basis	5.0		5.0
Net (gain) loss due to change in fair value of assets measured on nonrecurring basis			$ 0.1