Fair Value Measurements (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011
Fair Value Measurements (Textual) [Abstract]
Notice Period to redeem quarterly investments (in days)	45 days
Private equity funds [Member]
Fair Value Estimate Not Practicable (Textual)
Liquidation period of funds, minimum (in years)	1 year
Liquidation period of funds, maximum (in years)	10 years
Passive Funds [Member]
Fair Value Estimate Not Practicable (Textual)
Liquidation period of funds, minimum (in years)	1 year
Liquidation period of funds, maximum (in years)	7 years
Co Managed Funds [Member]
Fair Value Estimate Not Practicable (Textual)
Maturity Period of funds, minimum (in Years)	3 years
Maturity Period of funds, maximum (in Years)	6 years
Principal Investments [Member]
Fair values of the direct and indirect funds and the direct and indirect unfunded commitments for funds [Abstract]
Fair Value	473
Unfunded Commitments	123
Principal Investments [Member] | Private equity funds [Member]
Fair values of the direct and indirect funds and the direct and indirect unfunded commitments for funds [Abstract]
Fair Value	468
Unfunded Commitments	123
Principal Investments [Member] | Hedge funds [Member]
Fair values of the direct and indirect funds and the direct and indirect unfunded commitments for funds [Abstract]
Fair Value	5
Unfunded Commitments	0
Private Equity and Mezzanine Investments [Member]
Fair values of the direct and indirect funds and the direct and indirect unfunded commitments for funds [Abstract]
Fair Value	36
Unfunded Commitments	10
Private Equity and Mezzanine Investments [Member] | Passive Funds [Member]
Fair values of the direct and indirect funds and the direct and indirect unfunded commitments for funds [Abstract]
Fair Value	17
Unfunded Commitments	4
Private Equity and Mezzanine Investments [Member] | Co Managed Funds [Member]
Fair values of the direct and indirect funds and the direct and indirect unfunded commitments for funds [Abstract]
Fair Value	19
Unfunded Commitments	6