Fair Value Measurement - Quantitative Information - Liabilities (Details) - Valuation, Income Approach [Member] - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2019	Dec. 31, 2018
Credit derivative liabilities, net [Member] | Level 3 [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total liabilities carried at fair value	$ (161)	$ (185)
Credit derivative liabilities, net [Member] | Minimum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Internal floor (as a percent)	0.09%		0.30%
Bank profit (as a percent)	0.44%		0.51%
Hedge cost (as a percent)	0.21%		0.05%
Credit derivative liabilities, net [Member] | Minimum [Member] | Level 3 [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Year 1 loss estimates (as a percent)	0.00%	0.00%
Credit derivative liabilities, net [Member] | Maximum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Internal floor (as a percent)	0.30%
Bank profit (as a percent)	2.89%		2.12%
Hedge cost (as a percent)	1.19%		0.31%
Credit derivative liabilities, net [Member] | Maximum [Member] | Level 3 [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Year 1 loss estimates (as a percent)	83.00%	46.00%
Credit derivative liabilities, net [Member] | Weighted Average [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Internal floor (as a percent)	0.09%
Bank profit (as a percent)	1.07%		0.76%
Hedge cost (as a percent)	0.44%		0.11%
Credit derivative liabilities, net [Member] | Weighted Average [Member] | Level 3 [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Year 1 loss estimates (as a percent)	2.10%	1.30%
Financial Guaranty Variable Interest Entities [Member] | Level 3 [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total liabilities carried at fair value	$ (352)	$ (469)
Financial Guaranty Variable Interest Entities [Member] | Minimum [Member] | Level 3 [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)	1.90%	2.70%
Financial Guaranty Variable Interest Entities [Member] | Maximum [Member] | Level 3 [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)	8.30%	8.40%
Financial Guaranty Variable Interest Entities [Member] | Weighted Average [Member] | Level 3 [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)	4.60%	4.20%
Liabilities of Consolidated Investment Vehicles [Member] | Level 3 [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total liabilities carried at fair value	$ (806)	$ (481)
Yield (as a percent)	2.60%	10.00%
Liabilities of Consolidated Investment Vehicles [Member] | Maximum [Member] | Level 3 [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)	13.40%
Liabilities of Consolidated Investment Vehicles [Member] | Weighted Average [Member] | Level 3 [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)	3.00%
Corporate securities [Member] | Level 3 [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)	45.30%	35.90%
Measurement Input, Revenue Multiple [Member] | Assets of Consolidated Investment Vehicles [Member] | Minimum [Member] | Level 3 [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Transferor's continuing involvement, servicing assets or liabilities, prepayment speed
Measurement Input, Revenue Multiple [Member] | Assets of Consolidated Investment Vehicles [Member] | Maximum [Member] | Level 3 [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Transferor's continuing involvement, servicing assets or liabilities, prepayment speed
Measurement Input, Revenue Multiple [Member] | Debt Securities [Member] | Level 3 [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Transferor's continuing involvement, servicing assets or liabilities, prepayment speed	66.00%	50.00%
Measurement Input, Revenue Multiple [Member] | Equity Securities and Warrants [Member] | Level 3 [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Transferor's continuing involvement, servicing assets or liabilities, prepayment speed	66.00%	50.00%
Measurement Input, Prepayment Rate [Member] | Financial Guaranty Variable Interest Entities [Member] | Minimum [Member] | Level 3 [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Transferor's continuing involvement, servicing assets or liabilities, prepayment speed	0.40%	0.10%
Measurement Input, Prepayment Rate [Member] | Financial Guaranty Variable Interest Entities [Member] | Maximum [Member] | Level 3 [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Transferor's continuing involvement, servicing assets or liabilities, prepayment speed	18.80%	18.60%
Measurement Input, Prepayment Rate [Member] | Financial Guaranty Variable Interest Entities [Member] | Weighted Average [Member] | Level 3 [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Transferor's continuing involvement, servicing assets or liabilities, prepayment speed	8.60%	8.60%
Measurement Input, Default Rate [Member] | Financial Guaranty Variable Interest Entities [Member] | Minimum [Member] | Level 3 [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Transferor's continuing involvement, servicing assets or liabilities, prepayment speed	1.20%	1.20%
Measurement Input, Default Rate [Member] | Financial Guaranty Variable Interest Entities [Member] | Maximum [Member] | Level 3 [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Transferor's continuing involvement, servicing assets or liabilities, prepayment speed	26.50%	24.70%
Measurement Input, Default Rate [Member] | Financial Guaranty Variable Interest Entities [Member] | Weighted Average [Member] | Level 3 [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Transferor's continuing involvement, servicing assets or liabilities, prepayment speed	5.30%	4.90%
Measurement Input, Loss Severity [Member] | Financial Guaranty Variable Interest Entities [Member] | Minimum [Member] | Level 3 [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Transferor's continuing involvement, servicing assets or liabilities, prepayment speed	45.00%	40.00%
Measurement Input, Loss Severity [Member] | Financial Guaranty Variable Interest Entities [Member] | Maximum [Member] | Level 3 [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Transferor's continuing involvement, servicing assets or liabilities, prepayment speed	100.00%	100.00%
Measurement Input, Loss Severity [Member] | Financial Guaranty Variable Interest Entities [Member] | Weighted Average [Member] | Level 3 [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Transferor's continuing involvement, servicing assets or liabilities, prepayment speed	79.70%	76.10%
Measurement Input, EBITDA Multiple [Member] | Debt Securities [Member] | Level 3 [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Transferor's continuing involvement, servicing assets or liabilities, prepayment speed	100.00%	950.00%
Measurement Input, EBITDA Multiple [Member] | Equity Securities and Warrants [Member] | Level 3 [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Transferor's continuing involvement, servicing assets or liabilities, prepayment speed		950.00%
Measurement Input, EBITDA Multiple [Member] | Equity Securities and Warrants [Member] | Minimum [Member] | Level 3 [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Transferor's continuing involvement, servicing assets or liabilities, prepayment speed	810.00%
Measurement Input, EBITDA Multiple [Member] | Equity Securities and Warrants [Member] | Maximum [Member] | Level 3 [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Transferor's continuing involvement, servicing assets or liabilities, prepayment speed	100.00%