CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY (USD $) In Millions, except Share data, unless otherwise specified	Total	Common stock	Retained earnings	Accumulated other comprehensive income (loss)	Nonredeemable noncontrolling interests
Balance at Dec. 31, 2011	$ 1,349.1	$ 1.9	$ 1,311.8	$ (0.5)	$ 35.9
Balance (in shares) at Dec. 31, 2011		187,000,000
Increase (Decrease) in Stockholders' Equity
Net income	72.5		71.1		1.4
Other comprehensive (income) loss	0.6			0.6
Amortization of stock-based compensation	24.0		20.5		3.5
Issuance and forfeitures of restricted stock awards, net (in shares)		1,300,000
Stock option exercises and employee stock purchases	5.3		5.3
Stock option exercises and employee stock purchases (in shares)		900,000
Stock option issuance	4.9		4.9
Change in noncontrolling interests in consolidated investment products	(16.5)				(16.5)
Distributions to noncontrolling interests	(1.8)				(1.8)
Change in fair value of redeemable noncontrolling interests	22.1		22.1
Vesting of noncontrolling interests	(1.2)				(1.2)
Purchase of noncontrolling interests	(0.6)				(0.6)
Common stock repurchases	(14.9)		(14.9)
Common stock repurchases (in shares)		(1,800,000)
Common stock dividends	(31.9)		(31.9)
Balance at Sep. 30, 2012	1,411.6	1.9	1,388.9	0.1	20.7
Balance (in shares) at Sep. 30, 2012		187,400,000
Balance at Dec. 31, 2012	1,435.1	1.9	1,415.4	0.6	17.2
Balance (in shares) at Dec. 31, 2012	187,522,000	187,500,000
Increase (Decrease) in Stockholders' Equity
Net income	77.2		76.4		0.8
Other comprehensive (income) loss	(1.8)			(1.8)
Amortization of stock-based compensation	17.8		16.1		1.7
Issuance and forfeitures of restricted stock awards, net (in shares)		3,000,000
Stock option exercises and employee stock purchases	7.1		7.1
Stock option exercises and employee stock purchases (in shares)		1,300,000
Convertible senior notes issuance	14.7		14.7
Extinguishment of convertible senior notes	(2.0)		(2.0)
Convertible note hedge issuance	(16.1)		(16.1)
Stock warrants issuance	10.5		10.5
Change in noncontrolling interests in consolidated investment products	21.5				21.5
Distributions to noncontrolling interests	(1.6)				(1.6)
Change in fair value of redeemable noncontrolling interests	1.7		1.7
Vesting of noncontrolling interests	(1.2)				(1.2)
Purchase of noncontrolling interests	(0.3)				(0.3)
Common stock repurchases	(22.2)		(22.2)
Common stock repurchases (in shares)		(2,500,000)
Common stock dividends	(26.5)		(26.5)
Balance at Sep. 30, 2013	$ 1,513.9	$ 1.9	$ 1,475.1	$ (1.2)	$ 38.1
Balance (in shares) at Sep. 30, 2013	189,347,010	189,300,000