Variable Interest Entities (Details 2) (USD $)	Jun. 30, 2012	Dec. 31, 2011
Sponsored Investment Funds
Total assets of unconsolidated money market mutual fund variable interest entities	$ 1,500,000,000	$ 1,700,000,000
Other investments: Other limited partnership interests
Unconsolidated Variable Interest Entity disclosures
Asset carrying value	126,300,000	122,100,000
Maximum exposure to loss	126,300,000	122,100,000
Available-for-sale | Corporate debt securities
Unconsolidated Variable Interest Entity disclosures
Asset carrying value	526,800,000	544,000,000
Maximum exposure to loss	396,300,000	392,600,000
Available-for-sale | Residential mortgage-backed pass-through securities
Unconsolidated Variable Interest Entity disclosures
Asset carrying value	3,298,200,000	3,343,000,000
Maximum exposure to loss	3,095,700,000	3,155,800,000
Available-for-sale | Commercial mortgage-backed securities
Unconsolidated Variable Interest Entity disclosures
Asset carrying value	3,744,900,000	3,413,700,000
Maximum exposure to loss	4,128,100,000	3,894,300,000
Available-for-sale | Collateralized debt obligations
Unconsolidated Variable Interest Entity disclosures
Asset carrying value	366,100,000	338,800,000
Maximum exposure to loss	438,400,000	399,700,000
Available-for-sale | Other debt obligations
Unconsolidated Variable Interest Entity disclosures
Asset carrying value	3,480,200,000	3,570,200,000
Maximum exposure to loss	3,525,500,000	3,606,900,000
Trading | Residential mortgage-backed pass-through securities
Unconsolidated Variable Interest Entity disclosures
Asset carrying value	103,300,000	105,600,000
Maximum exposure to loss	103,300,000	105,600,000
Trading | Commercial mortgage-backed securities
Unconsolidated Variable Interest Entity disclosures
Asset carrying value	3,500,000	12,000,000
Maximum exposure to loss	3,500,000	12,000,000
Trading | Collateralized debt obligations
Unconsolidated Variable Interest Entity disclosures
Asset carrying value	50,600,000	51,400,000
Maximum exposure to loss	50,600,000	51,400,000
Trading | Other debt obligations
Unconsolidated Variable Interest Entity disclosures
Asset carrying value	16,900,000	64,900,000
Maximum exposure to loss	$ 16,900,000	$ 64,900,000