Related Parties (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015	Dec. 31, 2014
Investment Advisory Fees	$ 946.7	$ 1,055.7	$ 1,860.3	$ 2,057.1
Distribution and Servicing Fees	203.4	219.6	401.1	433.0
Performance Fees	8.9	6.7	23.4	53.5
Revenue, Other Financial Services	30.4	36.1	53.3	66.1
Revenues	1,189.4	1,318.1	2,338.1	2,609.7
Cash and cash equivalents	1,446.2	1,465.7	1,446.2	1,465.7	$ 1,851.4	$ 1,514.2
Unsettled fund receivables	1,202.9		1,202.9		566.3
Accounts receivable	516.2		516.2		528.1
Investments	892.0		892.0		1,019.1
Separate Account Assets	6,620.4		6,620.4		6,051.5
Other assets	68.8		68.8		107.0
Total assets	23,502.8		23,502.8		25,073.2
Accrued compensation and benefits	412.1		412.1		661.3
Accounts payable and accrued expenses	928.4		928.4		863.1
Unsettled fund payables	1,192.8		1,192.8		561.9
Total liabilities	15,460.1		15,460.1		16,210.2
Affiliated Entity [Member]
Investment Advisory Fees	820.1	927.7	1,617.0	1,809.1
Distribution and Servicing Fees	203.1	219.6	400.6	431.6
Performance Fees	6.4	1.5	16.8	12.3
Revenue, Other Financial Services	24.7	30.4	46.5	58.0
Revenues	1,054.3	$ 1,179.2	2,080.9	$ 2,311.0
Cash and cash equivalents	328.1		328.1		383.3
Unsettled fund receivables	321.8		321.8		166.7
Accounts receivable	310.6		310.6		317.7
Investments	847.3		847.3		982.7
Separate Account Assets	6,620.1		6,620.1		6,051.2
Other assets	2.1		2.1		3.4
Total assets	8,430.0		8,430.0		7,905.0
Accrued compensation and benefits	82.6		82.6		105.0
Accounts payable and accrued expenses	94.6		94.6		82.9
Unsettled fund payables	799.9		799.9		248.2
Total liabilities	$ 977.1		$ 977.1		$ 436.1