Investments (excluding Consolidated Investment Entities) - OTTI OCI (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Other than Temporary Impairment, Recognized in Accumulated Other Comprehensive Income [Roll Forward]
Balance, beginning	$ 80.2	$ 104.0	$ 86.8	$ 114.2
Additional credit impairments:
On securities not previously impaired	0.0	0.3	0.0	1.4
On securities previously impaired	0.6	1.7	3.4	3.2
Reductions:
Increase in cash flows	0.1	0.0	0.9	0.0
Securities sold, matured, prepaid, or paid down	3.0	3.6	11.6	16.4
Balance, ending	$ 77.7	$ 102.4	$ 77.7	$ 102.4