Related Parties (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Cash and cash equivalents	$ 1,514.2	$ 1,331.2	$ 835.5	$ 727.4
Investment Advisory Fees	4,054.1	3,599.6	3,127.8
Distribution and Servicing Fees	893.1	872.8	771.6
Performance Fees	61.1	55.9	41.4
Revenue, Other Financial Services	138.8	116.3	109.6
Revenues	5,147.1	4,644.6	4,050.4
Unsettled fund receivables	732.4	932.4
Accounts receivable	545.9	500.8
Investments	885.4	839.7
Separate Account Assets	1,697.9	1,416.0
Other assets	92.0	182.1
Total assets	20,462.5	19,270.5
Accrued compensation and benefits	667.3	676.4
Accounts payable and accrued expenses	757.3	763.1
Unsettled fund payables	730.1	882.0
Total liabilities	11,177.2	10,293.2
Affiliated Entity [Member]
Cash and cash equivalents	474.9	447.8
Investment Advisory Fees	3,609.8	3,208.2	2,754.2
Distribution and Servicing Fees	880.5	856.4	752.0
Performance Fees	39.0	44.0	32.6
Revenue, Other Financial Services	120.5	108.5	101.6
Revenues	4,649.8	4,217.1	3,640.4
Unsettled fund receivables	254.2	315.5
Accounts receivable	332.9	298.5
Investments	848.8	789.8
Separate Account Assets	1,697.5	1,415.7
Other assets	7.9	5.4
Total assets	3,616.2	3,272.7
Accrued compensation and benefits	138.8	151.6
Accounts payable and accrued expenses	61.9	19.5
Unsettled fund payables	322.1	389.9
Total liabilities	$ 522.8	$ 561.0