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, 2013	Mar. 31, 2012
Mortgage loans
Assets and liabilities measured at fair value on a nonrecurring basis
Fair value of assets measured on nonrecurring basis	$ 64.2	$ 126.5
Net (gain) loss due to change in fair value of assets measured on nonrecurring basis	3.6	7.9
Mortgage loans | Minimum
Assets and liabilities measured at fair value on a nonrecurring basis
Discount rate (as a percent)	10.30%	8.00%
Terminal capitalization rate (as a percent)	8.00%	6.30%
Average market rent growth rate (as a percent)	1.00%	8.00%
Mortgage loans | Maximum
Assets and liabilities measured at fair value on a nonrecurring basis
Discount rate (as a percent)	20.00%	13.00%
Terminal capitalization rate (as a percent)	10.50%	10.30%
Average market rent growth rate (as a percent)	5.00%	13.00%
Mortgage servicing rights
Assets and liabilities measured at fair value on a nonrecurring basis
Fair value of assets measured on nonrecurring basis	6.9	4.4
Net (gain) loss due to change in fair value of assets measured on nonrecurring basis	$ (0.2)	$ (0.1)
Mortgage servicing rights | Input
Assets and liabilities measured at fair value on a nonrecurring basis
Discount rate (as a percent)	3.20%	3.30%