Fair Value of Financial Instruments - Quantitative Information About Significant Unobservable Inputs (Details) $ in Millions	Sep. 30, 2021 USD ($)	Dec. 31, 2020 USD ($)
Sales restrictions discount | Equity warrant asset, public portfolio | Upper Limit
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Weighted  Average	0.20
Level 3 | Equity warrant asset, public portfolio
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair value	$ 4	$ 1
Level 3 | Equity warrant assets, private portfolio
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair value	$ 261	$ 191
Level 3 | Volatility | Equity warrant asset, public portfolio | Lower Limit
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Weighted  Average	0.282	0.460
Level 3 | Volatility | Equity warrant asset, public portfolio | Upper Limit
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Weighted  Average	0.569	0.568
Level 3 | Volatility | Equity warrant asset, public portfolio | Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Weighted  Average	0.504	0.491
Level 3 | Volatility | Equity warrant assets, private portfolio | Lower Limit
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Weighted  Average	0.258	0.244
Level 3 | Volatility | Equity warrant assets, private portfolio | Upper Limit
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Weighted  Average	0.569	0.568
Level 3 | Volatility | Equity warrant assets, private portfolio | Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Weighted  Average	0.439	0.432
Level 3 | Risk-Free interest rate | Equity warrant asset, public portfolio | Lower Limit
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Weighted  Average	0.0004	0.003
Level 3 | Risk-Free interest rate | Equity warrant asset, public portfolio | Upper Limit
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Weighted  Average	0.015	0.009
Level 3 | Risk-Free interest rate | Equity warrant asset, public portfolio | Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Weighted  Average	0.012	0.006
Level 3 | Risk-Free interest rate | Equity warrant assets, private portfolio | Lower Limit
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Weighted  Average	0.0004	0.0001
Level 3 | Risk-Free interest rate | Equity warrant assets, private portfolio | Upper Limit
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Weighted  Average	0.0116	0.0052
Level 3 | Risk-Free interest rate | Equity warrant assets, private portfolio | Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Weighted  Average	0.004	0.001
Level 3 | Sales restrictions discount | Equity warrant asset, public portfolio
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Weighted  Average	0.100
Level 3 | Sales restrictions discount | Equity warrant asset, public portfolio | Lower Limit
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Weighted  Average	0.10	0.100
Level 3 | Sales restrictions discount | Equity warrant asset, public portfolio | Upper Limit
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Weighted  Average	0.20	0.200
Level 3 | Sales restrictions discount | Equity warrant asset, public portfolio | Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Weighted  Average	0.167	0.102
Level 3 | Marketability discount | Equity warrant assets, private portfolio
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Weighted  Average	0.208	0.206
Level 3 | Marketability discount | Equity warrant assets, private portfolio | Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Weighted  Average	0.208	0.206
Level 3 | Remaining life assumption | Equity warrant assets, private portfolio
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Weighted  Average	0.400	0.400
Level 3 | Remaining life assumption | Equity warrant assets, private portfolio | Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Weighted  Average	0.400	0.400