Off-Balance Sheet Arrangements, Guarantees and Other Commitments - Total Capital Commitments, Unfunded Capital Commitments, and Our Ownership in Each Fund (Additional Information) (Detail) - Other fund investments - Consolidated venture capital and private equity fund investments	9 Months Ended
	Sep. 30, 2018 Investment
Venture Capital and Private Equity Fund Investments [Line Items]
Number of other funds with investment commitments	223
Upper Limit
Venture Capital and Private Equity Fund Investments [Line Items]
Percentage of ownership	5.00%