Guarantor Condensed Consolidating Financial Statements (Condensed Consolidating Statements Of Income) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Operating revenues:
Investment management fees	$ 3,138.5	$ 2,720.9	$ 2,120.2
Performance fees	37.9	26.1	30.0
Other	135.5	95.2	64.5
Total operating revenues	4,092.2	3,487.7	2,627.3
Operating expenses:
Employee compensation	1,246.2	1,114.9	950.8
Third-party distribution, service and advisory	1,282.5	1,053.8	737.0
Marketing	86.0	78.5	65.3
Property, office and technology	254.6	238.4	212.3
General and administrative	295.4	262.2	166.8
Transaction and integration	29.4	150.0
Total operating expenses	3,194.1	2,897.8	2,143.0
Operating income/(loss)	898.1	589.9	484.3
Other income/(expense):
Equity in earnings of unconsolidated affiliates	30.5	40.2	27.0
Interest and dividend income	11.0	10.4	9.8
Interest income of consolidated investment products	307.2	240.9	0
Other gains/(losses) of consolidated investment products, net	(138.9)	114.0	(106.9)
Interest expense	(61.8)	(58.6)	(64.5)
Interest expense of consolidated investment products	(187.0)	(118.6)	0
Other gains and losses, net	49.0	15.6	7.8
Income before income taxes	908.1	833.8	357.5
Income tax provision	(286.1)	(197.0)	(148.2)
Net income	622.0	636.8	209.3
(Gains)/losses attributable to noncontrolling interests in consolidated entities, net	107.7	(171.1)	113.2
Net income attributable to common shareholders	729.7	465.7	322.5
Guarantors [Member]
Operating revenues:
Investment management fees	1,153.9	906.0	482.0
Service and distribution fees	91.9	86.5	49.0
Performance fees	11.4	2.4	0.2
Other	15.2	4.1	2.4
Intercompany Revenues	27.1	32.6	16.1
Total operating revenues	1,299.5	1,031.6	549.7
Operating expenses:
Employee compensation	341.5	311.9	214.5
Third-party distribution, service and advisory	89.7	42.8	3.2
Marketing	5.1	35.6	23.8
Property, office and technology	105.1	107.2	52.8
General and administrative	81.5	97.5	81.5
Transaction and integration	0	0	0
Intercompany Expenses	175.8	147.4	56.3
Total operating expenses	798.7	742.4	432.1
Operating income/(loss)	500.8	289.2	117.6
Other income/(expense):
Equity in earnings of unconsolidated affiliates	(0.4)	5.7	17.1
Interest and dividend income	3.5	0.6	0.7
Interest income of consolidated investment products	0	0	0
Other gains/(losses) of consolidated investment products, net	0	0	(0.4)
Interest expense	(136.3)	(113.3)	(51.9)
Interest expense of consolidated investment products	0	0	0
Other gains and losses, net	44.6	2.9	(0.6)
Income before income taxes	412.2	185.1	82.5
Income tax provision	(111.5)	(66.1)	(0.2)
Net income	300.7	119.0	82.3
(Gains)/losses attributable to noncontrolling interests in consolidated entities, net	0	0	0
Net income attributable to common shareholders	300.7	119.0	82.3
Non-Guarantors [Member]
Operating revenues:
Investment management fees	1,984.6	1,814.9	1,638.2
Service and distribution fees	688.4	559.0	363.6
Performance fees	26.5	23.7	29.8
Other	120.3	91.1	62.1
Intercompany Revenues	176.3	147.7	52.2
Total operating revenues	2,996.1	2,636.4	2,145.9
Operating expenses:
Employee compensation	897.5	796.6	729.5
Third-party distribution, service and advisory	1,192.8	1,011.0	733.8
Marketing	80.9	42.8	41.5
Property, office and technology	148.8	130.4	159.2
General and administrative	207.7	157.1	78.7
Transaction and integration	29.4	150.0	10.8
Intercompany Expenses	27.1	32.6	16.1
Total operating expenses	2,584.2	2,320.5	1,769.6
Operating income/(loss)	411.9	315.9	376.3
Other income/(expense):
Equity in earnings of unconsolidated affiliates	29.6	33.4	53.3
Interest and dividend income	87.2	96.7	42.5
Interest income of consolidated investment products	307.2	240.9	0
Other gains/(losses) of consolidated investment products, net	(138.9)	114.0	(125.6)
Interest expense	(1.0)	(1.8)	(0.2)
Interest expense of consolidated investment products	(187.0)	(118.6)	0
Other gains and losses, net	3.4	16.6	1.0
Income before income taxes	512.4	697.1	347.3
Income tax provision	(161.0)	(129.2)	(136.5)
Net income	351.4	567.9	210.8
(Gains)/losses attributable to noncontrolling interests in consolidated entities, net	107.7	(171.1)	113.2
Net income attributable to common shareholders	459.1	396.8	324.0
Issuer [Member]
Operating revenues:
Investment management fees	0	0	0
Service and distribution fees	0	0	0
Performance fees	0	0	0
Other	0	0	0
Intercompany Revenues	0	0	4.7
Total operating revenues	0	0	4.7
Operating expenses:
Employee compensation	0	0	0
Third-party distribution, service and advisory	0	0	0
Marketing	0	0	0
Property, office and technology	0	0	0
General and administrative	0	0	1.4
Transaction and integration	0	0	0
Intercompany Expenses	0	0	0
Total operating expenses	0	0	1.4
Operating income/(loss)	0	0	3.3
Other income/(expense):
Equity in earnings of unconsolidated affiliates	453.9	266.5	148.3
Interest and dividend income	49.3	17.4	12.8
Interest income of consolidated investment products	0	0	0
Other gains/(losses) of consolidated investment products, net	0	0	21.5
Interest expense	(50.3)	(60.1)	(68.1)
Interest expense of consolidated investment products	0	0	0
Other gains and losses, net	(1.4)	0.8	5.4
Income before income taxes	451.5	224.6	123.2
Income tax provision	(13.6)	2.3	(11.5)
Net income	437.9	226.9	111.7
(Gains)/losses attributable to noncontrolling interests in consolidated entities, net	0	0	0
Net income attributable to common shareholders	437.9	226.9	111.7
Parent Company [Member]
Operating revenues:
Investment management fees	0	0	0
Service and distribution fees	0	0	0
Performance fees	0	0	0
Other	0	0	0
Intercompany Revenues	0	0	0
Total operating revenues	0	0	0
Operating expenses:
Employee compensation	7.2	6.4	6.8
Third-party distribution, service and advisory	0	0	0
Marketing	0	0.1	0
Property, office and technology	0.7	0.8	0.3
General and administrative	6.2	7.6	5.2
Transaction and integration	0	0	0
Intercompany Expenses	0.5	0.3	0.6
Total operating expenses	14.6	15.2	12.9
Operating income/(loss)	(14.6)	(15.2)	(12.9)
Other income/(expense):
Equity in earnings of unconsolidated affiliates	745.1	477.3	326.3
Interest and dividend income	0.9	13.4	9.5
Interest income of consolidated investment products	0	0	0
Other gains/(losses) of consolidated investment products, net	0	0	(2.4)
Interest expense	(4.1)	(1.1)	0
Interest expense of consolidated investment products	0	0	0
Other gains and losses, net	2.4	(4.7)	2.0
Income before income taxes	729.7	469.7	322.5
Income tax provision	0	(4.0)	0
Net income	729.7	465.7	322.5
(Gains)/losses attributable to noncontrolling interests in consolidated entities, net	0	0	0
Net income attributable to common shareholders	729.7	465.7	322.5
Adjustments [Member]
Operating revenues:
Investment management fees	0	0	0
Service and distribution fees	0	0	0
Performance fees	0	0	0
Other	0	0	0
Intercompany Revenues	(203.4)	(180.3)	(73.0)
Total operating revenues	(203.4)	(180.3)	(73.0)
Operating expenses:
Employee compensation	0	0	0
Third-party distribution, service and advisory	0	0	0
Marketing	0	0	0
Property, office and technology	0	0	0
General and administrative	0	0	0
Transaction and integration	0	0	0
Intercompany Expenses	(203.4)	(180.3)	(73.0)
Total operating expenses	(203.4)	(180.3)	(73.0)
Operating income/(loss)	0	0	0
Other income/(expense):
Equity in earnings of unconsolidated affiliates	(1,197.7)	(742.7)	(518.0)
Interest and dividend income	(129.9)	(117.7)	(55.7)
Interest income of consolidated investment products	0	0	0
Other gains/(losses) of consolidated investment products, net	0	0	0
Interest expense	129.9	117.7	55.7
Interest expense of consolidated investment products	0	0	0
Other gains and losses, net	0	0	0
Income before income taxes	(1,197.7)	(742.7)	(518.0)
Income tax provision	0	0	0
Net income	(1,197.7)	(742.7)	(518.0)
(Gains)/losses attributable to noncontrolling interests in consolidated entities, net	0	0	0
Net income attributable to common shareholders	(1,197.7)	(742.7)	(518.0)
Consolidated [Member]
Operating revenues:
Investment management fees	3,138.5	2,720.9	2,120.2
Service and distribution fees	780.3	645.5	412.6
Performance fees	37.9	26.1	30.0
Other	135.5	95.2	64.5
Intercompany Revenues	0	0	0
Total operating revenues	4,092.2	3,487.7	2,627.3
Operating expenses:
Employee compensation	1,246.2	1,114.9	950.8
Third-party distribution, service and advisory	1,282.5	1,053.8	737.0
Marketing	86.0	78.5	65.3
Property, office and technology	254.6	238.4	212.3
General and administrative	295.4	262.2	166.8
Transaction and integration	29.4	150.0	10.8
Intercompany Expenses	0	0	0
Total operating expenses	3,194.1	2,897.8	2,143.0
Operating income/(loss)	898.1	589.9	484.3
Other income/(expense):
Equity in earnings of unconsolidated affiliates	30.5	40.2	27.0
Interest and dividend income	11.0	10.4	9.8
Interest income of consolidated investment products	307.2	240.9	0
Other gains/(losses) of consolidated investment products, net	(138.9)	114.0	(106.9)
Interest expense	(61.8)	(58.6)	(64.5)
Interest expense of consolidated investment products	(187.0)	(118.6)	0
Other gains and losses, net	49.0	15.6	7.8
Income before income taxes	908.1	833.8	357.5
Income tax provision	(286.1)	(197.0)	(148.2)
Net income	622.0	636.8	209.3
(Gains)/losses attributable to noncontrolling interests in consolidated entities, net	107.7	(171.1)	113.2
Net income attributable to common shareholders	$ 729.7	$ 465.7	$ 322.5