Off-Balance Sheet Arrangements, Guarantees and Other Commitments - Total Capital Commitments, Unfunded Capital Commitments, and Our Ownership in Each Fund (Additional Information) (Details) - Investment	6 Months Ended	12 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Upper Limit
Venture Capital and Private Equity Fund Investments [Line Items]
Percentage of ownership	5.00%
Non-marketable securities | Consolidated venture capital and private equity fund investments | Equity method accounting | CP II, LP
Venture Capital and Private Equity Fund Investments [Line Items]
Percentage of ownership	5.10%	5.10%
Non-marketable securities | Consolidated venture capital and private equity fund investments | Equity method accounting | Other fund investments
Venture Capital and Private Equity Fund Investments [Line Items]
Number of other funds with investment commitments	215
Non-marketable securities | Consolidated venture capital and private equity fund investments | Equity method accounting | Other fund investments | Upper Limit
Venture Capital and Private Equity Fund Investments [Line Items]
Percentage of ownership	5.00%
Non-marketable securities | Consolidated venture capital and private equity fund investments | Direct ownership interest | Equity method accounting | CP II, LP
Venture Capital and Private Equity Fund Investments [Line Items]
Percentage of ownership	1.30%
Non-marketable securities | Consolidated venture capital and private equity fund investments | Indirect ownership interest | Equity method accounting | CP II, LP
Venture Capital and Private Equity Fund Investments [Line Items]
Percentage of ownership	3.80%