Related Parties (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015	Dec. 31, 2014
Investment Advisory Fees	$ 913.6	$ 1,001.4
Distribution and Servicing Fees	197.7	213.4
Performance Fees	14.5	46.8
Revenue, Other Financial Services	22.9	30.0
Revenues	1,148.7	1,291.6
Cash and cash equivalents	1,454.5	1,219.7	$ 1,851.4	$ 1,514.2
Unsettled fund receivables	957.3		566.3
Accounts receivable	513.9		528.1
Investments	919.6		1,019.1
Separate Account Assets	6,578.3		6,051.5
Other assets	78.0		107.0
Total assets	22,658.2		25,073.2
Accrued compensation and benefits	331.0		661.3
Accounts payable and accrued expenses	754.9		863.1
Unsettled fund payables	933.9		561.9
Total liabilities	14,288.4		16,210.2
Affiliated Entity [Member]
Investment Advisory Fees	796.9	881.4
Distribution and Servicing Fees	197.5	212.0
Performance Fees	10.4	10.8
Revenue, Other Financial Services	21.8	27.6
Revenues	1,026.6	$ 1,131.8
Cash and cash equivalents	272.2		383.3
Unsettled fund receivables	363.3		166.7
Accounts receivable	299.7		317.7
Investments	903.5		982.7
Separate Account Assets	6,577.9		6,051.2
Other assets	2.0		3.4
Total assets	8,418.6		7,905.0
Accrued compensation and benefits	84.4		105.0
Accounts payable and accrued expenses	84.8		82.9
Unsettled fund payables	484.4		248.2
Total liabilities	$ 653.6		$ 436.1