Commitments and Contingencies - Unfunded Commitments (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012
Operating Statistics [Line Items]
Total unfunded commitments	$ 2,379.9
Corporate Private Equity [Member]
Operating Statistics [Line Items]
Total unfunded commitments	1,964.1
Global Market Strategies [Member]
Operating Statistics [Line Items]
Total unfunded commitments	217.9
Real Assets [Member]
Operating Statistics [Line Items]
Total unfunded commitments	$ 197.9