Fair Value Measurements (Fair Value and Redemption Frequency) (Details) (USD $) In Millions	9 Months Ended
	Sep. 30, 2011		Jun. 30, 2011		Dec. 31, 2010
Unfunded Commitments
Total Fair Value	10.0				11.8
Equity Securities [Member]
Unfunded Commitments
Redemption Frequency	Immediate
Total Fair Value	4.0				4.4
Debt Securities [Member]
Unfunded Commitments				[1]
Redemption Frequency	Immediate	[1]
Total Fair Value	5.6	[1]			5.5	[1]
Money Market Funds [Member]
Unfunded Commitments				[2]
Redemption Frequency	Immediate	[2]
Total Fair Value	0.2	[2]			1.6	[2]
Multi Strategy Fund [Member]
Unfunded Commitments				[3]
Redemption Frequency	Immediate	[3]
Total Fair Value	$ 0.2	[3]			$ 0.3	[3]

[1] This category includes funds holding investments in U.S. Treasury obligations and U.S. investment grade bonds. Investments in this category can be redeemed immediately at the current net asset value per unit.

[2] This category includes investments in high-quality, short-term securities. Investments in this category can be redeemed immediately at the current net asset value per unit.

[3] This category includes a mix of actively managed funds holding investments in stocks, bonds and short-term investments in a mix of actively managed funds. Investments in this category can be redeemed immediately at the current net asset value per unit.