Variable Interest Entities (Details 2) (USD $)	12 Months Ended
	Dec. 31, 2010	Dec. 31, 2011
Sponsored Investment Funds
Total assets of unconsolidated money market mutual fund variable interest entities	$ 1,700,000,000	$ 1,700,000,000
Contribution to unconsolidated money market mutual fund variable interest entities	3,200,000
Other investments: Other limited partnership interests
Unconsolidated Variable Interest Entity disclosures
Asset carrying value	71,700,000	76,300,000
Maximum exposure to loss	71,700,000	76,300,000
Available-for-sale | Corporate debt securities
Unconsolidated Variable Interest Entity disclosures
Asset carrying value	429,000,000	544,000,000
Maximum exposure to loss	367,700,000	392,600,000
Available-for-sale | Residential mortgage-backed pass-through securities
Unconsolidated Variable Interest Entity disclosures
Asset carrying value	3,196,200,000	3,343,000,000
Maximum exposure to loss	3,077,900,000	3,155,800,000
Available-for-sale | Commercial mortgage-backed securities
Unconsolidated Variable Interest Entity disclosures
Asset carrying value	3,842,200,000	3,413,700,000
Maximum exposure to loss	4,424,900,000	3,894,300,000
Available-for-sale | Collateralized debt obligations
Unconsolidated Variable Interest Entity disclosures
Asset carrying value	293,000,000	338,800,000
Maximum exposure to loss	380,500,000	399,700,000
Available-for-sale | Other debt obligations
Unconsolidated Variable Interest Entity disclosures
Asset carrying value	3,114,100,000	3,570,200,000
Maximum exposure to loss	3,184,900,000	3,606,900,000
Trading | Residential mortgage-backed pass-through securities
Unconsolidated Variable Interest Entity disclosures
Asset carrying value	215,500,000	105,600,000
Maximum exposure to loss	215,500,000	105,600,000
Trading | Commercial mortgage-backed securities
Unconsolidated Variable Interest Entity disclosures
Asset carrying value	5,100,000	12,000,000
Maximum exposure to loss	5,100,000	12,000,000
Trading | Collateralized debt obligations
Unconsolidated Variable Interest Entity disclosures
Asset carrying value	87,200,000	51,400,000
Maximum exposure to loss	87,200,000	51,400,000
Trading | Other debt obligations
Unconsolidated Variable Interest Entity disclosures
Asset carrying value	118,800,000	64,900,000
Maximum exposure to loss	$ 118,800,000	$ 64,900,000