Fair Value Measurement - Quantitative Information - Assets (Details) - Valuation, Income Approach [Member] - Level 3 [Member] - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Obligations of state and political subdivisions [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Asset, fair value	$ 86	$ 107
Obligations of state and political subdivisions [Member] | Minimum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)	5.30%	4.50%
Obligations of state and political subdivisions [Member] | Maximum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)	41.40%	31.10%
Obligations of state and political subdivisions [Member] | Weighted Average [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)	16.90%	8.50%
Corporate securities [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Asset, fair value	$ 26	$ 41
Yield (as a percent)	51.70%	35.90%
RMBS [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Asset, fair value	$ 253	$ 308
RMBS [Member] | Minimum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)	5.70%	3.70%
RMBS [Member] | Maximum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)	8.10%	6.10%
RMBS [Member] | Weighted Average [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)	6.90%	4.80%
Life Insurance Transaction [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Asset, fair value	$ 321	$ 350
Yield (as a percent)	6.50%
Life Insurance Transaction [Member] | Minimum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)		5.80%
Collateralized loan obligations (CLO) /TruPS [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Asset, fair value	$ 240	$ 256
Collateralized loan obligations (CLO) /TruPS [Member] | Minimum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)	2.40%	2.50%
Collateralized loan obligations (CLO) /TruPS [Member] | Maximum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)	4.40%	4.10%
Collateralized loan obligations (CLO) /TruPS [Member] | Weighted Average [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)	3.00%	2.90%
Other Asset Backed Securities [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Asset, fair value	$ 35	$ 52
Yield (as a percent)	20.70%
Other Asset Backed Securities [Member] | Minimum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)		2.30%
Other Asset Backed Securities [Member] | Maximum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)		9.40%
Other Asset Backed Securities [Member] | Weighted Average [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)		9.30%
FG VIEs and other [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Asset, fair value	$ 368	$ 442
FG VIEs and other [Member] | Minimum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)	5.10%	3.00%
FG VIEs and other [Member] | Maximum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)	10.80%	8.40%
FG VIEs and other [Member] | Weighted Average [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)	7.20%	5.20%
Assets of Consolidated Investment Vehicles [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)		12.50%
Assets of Consolidated Investment Vehicles [Member] | Minimum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)	6.90%
Assets of Consolidated Investment Vehicles [Member] | Maximum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)	21.20%
Assets of Consolidated Investment Vehicles [Member] | Weighted Average [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)	12.70%
Other Assets [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Asset, fair value	$ 100	$ 52
Fair Value Inputs Term	10 years	10 years
Other Assets [Member] | Minimum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)	5.50%	5.10%
Other Assets [Member] | Maximum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)	6.30%	5.80%
Other Assets [Member] | Weighted Average [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)	5.90%	5.50%
Other invested assets [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Asset, fair value	$ 6	$ 6
Measurement Input, Prepayment Rate [Member] | RMBS [Member] | Minimum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Transferor's continuing involvement, servicing assets or liabilities, prepayment speed	3.30%	2.00%
Measurement Input, Prepayment Rate [Member] | RMBS [Member] | Maximum [Member]
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 [Member] | RMBS [Member] | Weighted Average [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Transferor's continuing involvement, servicing assets or liabilities, prepayment speed	6.40%	6.30%
Measurement Input, Prepayment Rate [Member] | FG VIEs and other [Member] | Minimum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Transferor's continuing involvement, servicing assets or liabilities, prepayment speed	0.10%	0.10%
Measurement Input, Prepayment Rate [Member] | FG VIEs and other [Member] | Maximum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Transferor's continuing involvement, servicing assets or liabilities, prepayment speed	18.70%	18.60%
Measurement Input, Prepayment Rate [Member] | FG VIEs and other [Member] | Weighted Average [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Transferor's continuing involvement, servicing assets or liabilities, prepayment speed	8.40%	8.60%
Measurement Input, Default Rate [Member] | RMBS [Member] | Minimum [Member]
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 [Member] | RMBS [Member] | Maximum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Transferor's continuing involvement, servicing assets or liabilities, prepayment speed	7.50%	7.00%
Measurement Input, Default Rate [Member] | RMBS [Member] | Weighted Average [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Transferor's continuing involvement, servicing assets or liabilities, prepayment speed	4.90%	4.90%
Measurement Input, Default Rate [Member] | FG VIEs and other [Member] | Minimum [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] | FG VIEs and other [Member] | Maximum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Transferor's continuing involvement, servicing assets or liabilities, prepayment speed	24.90%	24.70%
Measurement Input, Default Rate [Member] | FG VIEs and other [Member] | Weighted Average [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Transferor's continuing involvement, servicing assets or liabilities, prepayment speed	4.90%	4.90%
Measurement Input, Loss Severity [Member] | RMBS [Member] | Minimum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Transferor's continuing involvement, servicing assets or liabilities, prepayment speed	40.00%	40.00%
Measurement Input, Loss Severity [Member] | RMBS [Member] | Maximum [Member]
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 [Member] | RMBS [Member] | Weighted Average [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Transferor's continuing involvement, servicing assets or liabilities, prepayment speed	79.00%	78.80%
Measurement Input, Loss Severity [Member] | FG VIEs and other [Member] | Minimum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Transferor's continuing involvement, servicing assets or liabilities, prepayment speed	40.00%	40.00%
Measurement Input, Loss Severity [Member] | FG VIEs and other [Member] | Maximum [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] | FG VIEs and other [Member] | Weighted Average [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Transferor's continuing involvement, servicing assets or liabilities, prepayment speed	74.30%	76.10%
Measurement Input, Discount Rate [Member] | Assets of Consolidated Investment Vehicles [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Asset, fair value	$ 96	$ 64
Measurement Input, Discount Rate [Member] | Assets of Consolidated Investment Vehicles [Member] | Minimum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Transferor's continuing involvement, servicing assets or liabilities, prepayment speed	15.30%	16.00%
Measurement Input, Discount Rate [Member] | Assets of Consolidated Investment Vehicles [Member] | Maximum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Transferor's continuing involvement, servicing assets or liabilities, prepayment speed	27.60%	28.00%
Measurement Input, Discount Rate [Member] | Assets of Consolidated Investment Vehicles [Member] | Weighted Average [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Transferor's continuing involvement, servicing assets or liabilities, prepayment speed	21.80%	21.00%