Fair Value Measurement - Quantitative Information - Assets (Details) - Valuation, Income Approach - Level 3 - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Obligations of state and political subdivisions
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total assets carried at fair value	$ 93	$ 107
Obligations of state and political subdivisions | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)	5.30%	4.50%
Obligations of state and political subdivisions | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)	37.60%	31.10%
Obligations of state and political subdivisions | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)	13.20%	8.50%
Corporate securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total assets carried at fair value	$ 30	$ 41
Yield (as a percent)	44.90%	35.90%
RMBS
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total assets carried at fair value	$ 257	$ 308
RMBS | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)	3.70%	3.70%
RMBS | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)	6.50%	6.10%
RMBS | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)	4.70%	4.80%
Life insurance transactions
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total assets carried at fair value	$ 360	$ 350
Yield (as a percent)	5.40%
Life insurance transactions | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)		5.80%
CLOs
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total assets carried at fair value	$ 498	$ 256
CLOs | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)		2.50%
CLOs | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)		4.10%
CLOs | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)		2.90%
Others
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total assets carried at fair value	$ 39	$ 52
Others | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)	3.10%	2.30%
Others | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)	11.40%	9.40%
Others | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)	11.30%	9.30%
FG VIEs and other
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total assets carried at fair value	$ 314	$ 442
FG VIEs and other | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)	2.10%	3.00%
FG VIEs and other | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)	7.70%	8.40%
FG VIEs and other | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)	5.30%	5.20%
Other assets
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total assets carried at fair value	$ 65	$ 52
Fair Value Inputs Term	10 years	10 years
Other assets | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)	3.80%	5.10%
Other assets | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)	4.50%	5.80%
Other assets | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)	4.20%	5.50%
Other invested assets
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total assets carried at fair value	$ 6	$ 6
Measurement Input, Prepayment Rate | RMBS | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Transferor's continuing involvement, servicing assets or liabilities, prepayment speed	1.10%	2.00%
Measurement Input, Prepayment Rate | RMBS | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Transferor's continuing involvement, servicing assets or liabilities, prepayment speed	15.00%	15.00%
Measurement Input, Prepayment Rate | RMBS | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Transferor's continuing involvement, servicing assets or liabilities, prepayment speed	6.90%	6.30%
Measurement Input, Prepayment Rate | FG VIEs and other | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Transferor's continuing involvement, servicing assets or liabilities, prepayment speed	0.90%	0.10%
Measurement Input, Prepayment Rate | FG VIEs and other | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Transferor's continuing involvement, servicing assets or liabilities, prepayment speed	18.90%	18.60%
Measurement Input, Prepayment Rate | FG VIEs and other | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Transferor's continuing involvement, servicing assets or liabilities, prepayment speed	8.70%	8.60%
Measurement Input, Default Rate | RMBS | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Transferor's continuing involvement, servicing assets or liabilities, prepayment speed	1.50%	1.50%
Measurement Input, Default Rate | RMBS | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Transferor's continuing involvement, servicing assets or liabilities, prepayment speed	11.40%	7.00%
Measurement Input, Default Rate | RMBS | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Transferor's continuing involvement, servicing assets or liabilities, prepayment speed	6.10%	4.90%
Measurement Input, Default Rate | FG VIEs and other | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Transferor's continuing involvement, servicing assets or liabilities, prepayment speed	1.80%	1.20%
Measurement Input, Default Rate | FG VIEs and other | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Transferor's continuing involvement, servicing assets or liabilities, prepayment speed	25.60%	24.70%
Measurement Input, Default Rate | FG VIEs and other | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Transferor's continuing involvement, servicing assets or liabilities, prepayment speed	5.90%	4.90%
Measurement Input, Loss Severity | RMBS | Minimum
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 | RMBS | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Transferor's continuing involvement, servicing assets or liabilities, prepayment speed	125.00%	125.00%
Measurement Input, Loss Severity | RMBS | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Transferor's continuing involvement, servicing assets or liabilities, prepayment speed	83.50%	78.80%
Measurement Input, Loss Severity | FG VIEs and other | Minimum
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 | FG VIEs and other | Maximum
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 | FG VIEs and other | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Transferor's continuing involvement, servicing assets or liabilities, prepayment speed	79.90%	76.10%
Measurement Input, Discount Rate | CLOs | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)	0.90%
Measurement Input, Discount Rate | CLOs | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)	4.10%
Measurement Input, Discount Rate | CLOs | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)	1.90%
Assets of Consolidated Investment Vehicles | Corporate securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total assets carried at fair value	$ 62
Assets of Consolidated Investment Vehicles | Equity securities and warrants
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total assets carried at fair value	$ 43	$ 17
Yield (as a percent)	9.30%	12.50%
Assets of Consolidated Investment Vehicles | Measurement Input, Discount Rate | Corporate securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total assets carried at fair value		$ 47
Assets of Consolidated Investment Vehicles | Measurement Input, Discount Rate | Corporate securities | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)	15.30%
Transferor's continuing involvement, servicing assets or liabilities, prepayment speed		16.00%
Assets of Consolidated Investment Vehicles | Measurement Input, Discount Rate | Corporate securities | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)	22.80%
Transferor's continuing involvement, servicing assets or liabilities, prepayment speed		28.00%
Assets of Consolidated Investment Vehicles | Measurement Input, Discount Rate | Corporate securities | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)	18.40%
Transferor's continuing involvement, servicing assets or liabilities, prepayment speed		21.50%
Assets of Consolidated Investment Vehicles | Measurement Input, Discount Rate | Equity securities and warrants | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)	15.30%	16.00%
Assets of Consolidated Investment Vehicles | Measurement Input, Discount Rate | Equity securities and warrants | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)	27.20%	28.00%
Assets of Consolidated Investment Vehicles | Measurement Input, Discount Rate | Equity securities and warrants | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)	25.90%	20.80%