Fair Value of Financial Instruments - Quantitative Information About Significant Unobservable Inputs (Details) $ in Millions	Jun. 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	$ 12	$ 1
Level 3 | Equity warrant assets, private portfolio
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair value	$ 245	$ 191
Level 3 | Volatility | Equity warrant asset, public portfolio | Lower Limit
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Weighted  Average	0.482	0.460
Level 3 | Volatility | Equity warrant asset, public portfolio | Upper Limit
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Weighted  Average	0.585	0.568
Level 3 | Volatility | Equity warrant asset, public portfolio | Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Weighted  Average	0.490	0.491
Level 3 | Volatility | Equity warrant assets, private portfolio | Lower Limit
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Weighted  Average	0.254	0.244
Level 3 | Volatility | Equity warrant assets, private portfolio | Upper Limit
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Weighted  Average	0.585	0.568
Level 3 | Volatility | Equity warrant assets, private portfolio | Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Weighted  Average	0.463	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	0.012	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	0.0002	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	0.0105	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	0.200
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	0.200	0.102
Level 3 | Marketability discount | Equity warrant assets, private portfolio
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Weighted  Average	0.220	0.206
Level 3 | Marketability discount | Equity warrant assets, private portfolio | Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Weighted  Average	0.220	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