Related Parties (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016	Dec. 31, 2015
Investment Advisory Fees	$ 955.2	$ 913.6
Distribution and Servicing Fees	206.4	197.7
Performance Fees	11.3	14.5
Revenue, Other Financial Services	19.7	22.9
Revenues	1,192.6	1,148.7
Cash and cash equivalents	1,397.0	1,454.5	$ 1,328.0	$ 1,851.4
Unsettled fund receivables	944.2		672.9
Accounts receivable	531.5		544.2
Investments	689.3		795.3
Separate Account Assets	9,230.5		8,224.2
Other assets	88.0		95.0
Total assets	26,598.9		25,734.3
Accrued compensation and benefits	390.5		654.3
Accounts payable and accrued expenses	766.7		812.4
Unsettled fund payables	922.6		659.3
Total liabilities	18,558.0		17,838.8
Affiliated Entity [Member]
Investment Advisory Fees	832.1	796.9
Distribution and Servicing Fees	206.1	197.5
Performance Fees	8.3	10.4
Revenue, Other Financial Services	16.8	21.8
Revenues	1,063.3	$ 1,026.6
Cash and cash equivalents	478.4		476.2
Unsettled fund receivables	240.8		253.2
Accounts receivable	319.1		344.4
Investments	636.7		728.3
Separate Account Assets	9,230.1		8,224.2
Other assets	3.1		2.9
Total assets	10,908.2		10,029.2
Accrued compensation and benefits	113.7		76.5
Accounts payable and accrued expenses	95.0		94.7
Unsettled fund payables	352.9		318.7
Total liabilities	$ 561.6		$ 489.9