Related Party Transaction (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011	Dec. 31, 2010
Related Party Transaction [Line Items]
Investment management fees	$ 818.0	$ 779.5	$ 2,390.0	$ 2,390.9
Performance fees	3.0	2.6	38.9	14.0
Other	24.3	26.6	83.0	91.0
Total operating revenues	1,041.4	997.8	3,084.1	3,095.1
ASSETS
Cash equivalents	880.1	757.0	880.1	757.0	727.4	740.5
Unsettled fund receivables	596.0		596.0		444.4
Accounts receivable	406.1		406.1		424.4
Current investments	364.2		364.2		283.7
Assets held for policyholders	1,139.3		1,139.3		1,243.5
Other current assets	81.7		81.7		150.0
Non-current investments	223.5		223.5		200.8
Other non-current assets	17.2		17.2		17.9
Total assets	17,861.0		17,861.0		19,347.0
LIABILITIES
Unsettled fund payables	598.2		598.2		439.6
Other current liabilities	719.1		719.1		841.5
Other non-current liabilities	329.1		329.1		297.3
Total liabilities	8,663.6		8,663.6		10,209.4
Affiliated Entity [Member]
Related Party Transaction [Line Items]
Investment management fees	700.6	666.8	2,040.1	2,056.7
Service and distribution fees	181.6	189.0	557.4	598.7
Performance fees	2.0	0.8	33.8	10.0
Other	23.6	24.0	76.7	87.1
Total operating revenues	907.8	880.6	2,708.0	2,752.5
ASSETS
Cash equivalents	200.7		200.7		257.7
Unsettled fund receivables	152.1		152.1		178.8
Accounts receivable	220.4		220.4		247.8
Current investments	326.2		326.2		248.9
Assets held for policyholders	1,139.0		1,139.0		1,243.1
Other current assets	26.1		26.1		22.1
Non-current investments	210.5		210.5		184.5
Other non-current assets	1.9		1.9		1.9
Total assets	2,276.9		2,276.9		2,384.8
LIABILITIES
Unsettled fund payables	281.3		281.3		205.0
Other current liabilities	61.6		61.6		63.5
Other non-current liabilities	107.8		107.8		191.6
Total liabilities	$ 450.7		$ 450.7		$ 460.1