Consolidated Investment Products (Condensed Consolidating Statement Of Income Line Items Reflecting Impact Of Consolidation Of Investment Products Into The Condensed Consolidated Statements Of Income) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2012		Jun. 30, 2011		Jun. 30, 2012		Jun. 30, 2011
Total operating revenues	$ 1,009.0		$ 1,070.0		$ 2,042.7		$ 2,097.3
Total operating expenses	806.1		837.0		1,610.0		1,638.6
Operating income	202.9		233.0		432.7		458.7
Equity in earnings of unconsolidated affiliates	6.9		10.8		16.6		17.5
Interest and dividend income	70.9		82.2		142.3		158.5
Other investment income/(losses)	69.5		(58.7)		(33.8)		(136.3)
Interest expense	(60.3)		(62.5)		(119.5)		(118.7)
Income before income taxes	289.9		204.8		438.3		379.7
Income tax provision	(62.3)		(75.4)		(135.9)		(151.0)
Net income	227.6		129.4		302.4		228.7
Net (income)/loss attributable to noncontrolling interests in consolidated entities, net	(73.7)		53.6		45.4		131.8
Net income attributable to common shareholders	153.9		183.0		347.8		360.5
Gain for the consolidation of CLOs	(6.1)		5.1		(1.9)		15.0
Before Consolidation [Member]
Total operating revenues	1,019.5	[1]	1,082.1	[1]	2,063.6	[2]	2,120.5	[2]
Total operating expenses	791.4	[1]	833.4	[1]	1,589.2	[2]	1,631.3	[2]
Operating income	228.1	[1]	248.7	[1]	474.4	[2]	489.2	[2]
Equity in earnings of unconsolidated affiliates	9.7	[1]	10.5	[1]	16.0	[2]	18.4	[2]
Interest and dividend income	5.7	[1]	4.0	[1]	11.5	[2]	7.3	[2]
Other investment income/(losses)	(7.7)	[1]	6.0	[1]	10.8	[2]	13.9	[2]
Interest expense	(13.4)	[1]	(16.0)	[1]	(27.0)	[2]	(32.2)	[2]
Income before income taxes	222.4	[1]	253.2	[1]	485.7	[2]	496.6	[2]
Income tax provision	(62.3)	[1]	(75.4)	[1]	(135.9)	[2]	(151.0)	[2]
Net income	160.1	[1]	177.8	[1]	349.8	[2]	345.6	[2]
Net (income)/loss attributable to noncontrolling interests in consolidated entities, net	0	[1]	0	[1]	0	[2]	0.1	[2]
Net income attributable to common shareholders	160.1	[1]	177.8	[1]	349.8	[2]	345.7	[2]
Consolidated Investment Products [Member]
Total operating revenues	(10.5)		(12.1)		(20.9)		(23.2)
Total operating expenses	14.7		3.6		20.8		7.3
Operating income	(25.2)		(15.7)		(41.7)		(30.5)
Equity in earnings of unconsolidated affiliates	(2.8)		0.3		0.6		(0.9)
Interest and dividend income	65.2		78.2		130.8		151.2
Other investment income/(losses)	77.2		(64.7)		(44.6)		(150.2)
Interest expense	(46.9)		(46.5)		(92.5)		(86.5)
Income before income taxes	67.5		(48.4)		(47.4)		(116.9)
Income tax provision	0		0		0		0
Net income	67.5		(48.4)		(47.4)		(116.9)
Net (income)/loss attributable to noncontrolling interests in consolidated entities, net	(73.7)		53.6		45.4		131.7
Net income attributable to common shareholders	(6.2)		5.2		(2.0)		14.8
CLOs - VIEs [Member]
Total operating revenues	0		0		0		0
Total operating expenses	13.9		12.1		24.1		24.3
Operating income	(13.9)		(12.1)		(24.1)		(24.3)
Equity in earnings of unconsolidated affiliates	0		0		0		0
Interest and dividend income	68.7		79.8		137.7		154.0
Other investment income/(losses)	28.2		(73.8)		(40.6)		(210.6)
Interest expense	(50.4)		(48.1)		(99.4)		(89.3)
Income before income taxes	32.6		(54.2)		(26.4)		(170.2)
Income tax provision	0		0		0		0
Net income	32.6		(54.2)		(26.4)		(170.2)
Net (income)/loss attributable to noncontrolling interests in consolidated entities, net	(32.6)		54.2		26.4		170.2
Net income attributable to common shareholders	0		0		0		0
Other VIEs [Member]
Total operating revenues	0		0		0		0
Total operating expenses	0.2		0.2		0.5		0.5
Operating income	(0.2)		(0.2)		(0.5)		(0.5)
Equity in earnings of unconsolidated affiliates	0		0		0		0
Interest and dividend income	0		0		0		0
Other investment income/(losses)	1.8		0.6		0.9		0.9
Interest expense	0		0		0		0
Income before income taxes	1.6		0.4		0.4		0.4
Income tax provision	0		0		0		0
Net income	1.6		0.4		0.4		0.4
Net (income)/loss attributable to noncontrolling interests in consolidated entities, net	(1.6)		(0.4)		(0.4)		(0.4)
Net income attributable to common shareholders	0		0		0		0
VOEs [Member]
Total operating revenues	0		0.1		0		0.1
Total operating expenses	11.1		3.5		17.1		5.8
Operating income	(11.1)		(3.4)		(17.1)		(5.7)
Equity in earnings of unconsolidated affiliates	0		0		0		0
Interest and dividend income	0		0		0		0
Other investment income/(losses)	53.3		3.4		(3.0)		44.5
Interest expense	0		0		0		0
Income before income taxes	42.2		0		(20.1)		38.8
Income tax provision	0		0		0		0
Net income	42.2		0		(20.1)		38.8
Net (income)/loss attributable to noncontrolling interests in consolidated entities, net	(39.5)		(0.2)		19.4		(38.1)
Net income attributable to common shareholders	2.7		(0.2)		(0.7)		0.7
VIE Adjustments [Member]
Total operating revenues	(10.5)	[1],[3]	(12.2)	[1],[3]	(20.9)	[2],[3]	(23.3)	[2],[3]
Total operating expenses	(10.5)	[1],[3]	(12.2)	[1],[3]	(20.9)	[2],[3]	(23.3)	[2],[3]
Operating income	0	[1],[3]	0	[1],[3]	0	[2],[3]	0	[2],[3]
Equity in earnings of unconsolidated affiliates	(2.8)	[1],[3]	0.3	[1],[3]	0.6	[2],[3]	(0.9)	[2],[3]
Interest and dividend income	(3.5)	[1],[3]	(1.6)	[1],[3]	(6.9)	[2],[3]	(2.8)	[2],[3]
Other investment income/(losses)	(6.1)	[1],[3]	5.1	[1],[3]	(1.9)	[2],[3]	15.0	[2],[3]
Interest expense	3.5	[1],[3]	1.6	[1],[3]	6.9	[2],[3]	2.8	[2],[3]
Income before income taxes	(8.9)	[1],[3]	5.4	[1],[3]	(1.3)	[2],[3]	14.1	[2],[3]
Income tax provision	0	[1],[3]	0	[1],[3]	0	[2],[3]	0	[2],[3]
Net income	(8.9)	[1],[3]	5.4	[1],[3]	(1.3)	[2],[3]	14.1	[2],[3]
Net (income)/loss attributable to noncontrolling interests in consolidated entities, net	0	[1],[3]	0	[1],[3]	0	[2],[3]	0	[2],[3]
Net income attributable to common shareholders	$ (8.9)	[1],[3]	$ 5.4	[1],[3]	$ (1.3)	[2],[3]	$ 14.1	[2],[3]

[1] The Before Consolidation column includes the company’s equity interest in the investment products accounted for as equity method (private equity and real estate partnership funds) and available-for-sale investments (CLOs). Upon consolidation of the CLOs, the company’s and the CLOs’ accounting policies are effectively aligned, resulting in the reclassification of the company’s loss for the three months ended June 30, 2012 of $6.1 million (representing the decrease in the market value of the company’s holding in the consolidated CLOs) from other comprehensive income into other gains/losses (three months ended June 30, 2011: $5.1 million gain). The company’s loss (gain) on its investments in the CLOs (before consolidation) eliminates with the company’s share of the offsetting gain (loss) on the CLOs’ debt. The net income arising from consolidation of CLOs is therefore completely attributed to other investors in these CLOs, as the company’s share has been eliminated through consolidation.

[2] The Before Consolidation column includes the company’s equity interest in the investment products accounted for as equity method (private equity and real estate partnership funds) and available-for-sale investments (CLOs). Upon consolidation of the CLOs, the company’s and the CLOs’ accounting policies are effectively aligned, resulting in the reclassification of the company’s loss for the six months ended June 30, 2012 of $1.9 million (representing the decrease in the market value of the company’s holding in the consolidated CLOs) from other comprehensive income into other gains/losses (six months ended June 30, 2011: $15 million gain). The company’s loss (gain) on its investments in the CLOs (before consolidation) eliminates with the company’s share of the offsetting gain (loss) on the CLOs’ debt. The net income arising from consolidation of CLOs is therefore completely attributed to other investors in these CLOs, as the company’s share has been eliminated through consolidation.

[3] Adjustments include the elimination of intercompany transactions between the company and its consolidated investment products, primarily the elimination of management fees expensed by the funds and recorded as operating revenues (before consolidation) by the company.