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, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Mortgage loans
Assets and liabilities measured at fair value on a nonrecurring basis
Fair value of assets measured on nonrecurring basis	$ 101.6	$ 172.5	$ 101.6	$ 172.5
Net (gain) loss due to change in fair value of assets measured on nonrecurring basis	4.6	3.1	22.3	14.4
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)			7.50%	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)			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	7.6	5.6	7.6	5.6
Net (gain) loss due to change in fair value of assets measured on nonrecurring basis	0	0.2	1.3	0.3
Mortgage servicing rights | Input
Assets and liabilities measured at fair value on a nonrecurring basis
Discount rate (as a percent)			3.90%	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		$ 0.1