Investments (excluding Consolidated Investment Entities) - OTTI OCI (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Other than Temporary Impairment, Recognized in Accumulated Other Comprehensive Income [Roll Forward]
Balance, beginning	$ 71.6	$ 80.2	$ 75.3	$ 86.8
Additional credit impairments:
On securities previously impaired	0.6	0.6	3.4	3.4
Reductions:
Increase in cash flows	1.7	0.1	1.9	0.9
Securities sold, matured, prepaid, or paid down	2.8	3.0	9.1	11.6
Balance, ending	$ 67.7	$ 77.7	$ 67.7	$ 77.7