Fair Value Measurement - Quantitative Information - Assets (Details) - Valuation, Income Approach [Member] - Level 3 [Member] - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Obligations of state and political subdivisions [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Asset, fair value	$ 109	$ 99
Obligations of state and political subdivisions [Member] | Minimum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)	4.50%	4.50%
Obligations of state and political subdivisions [Member] | Maximum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)	32.30%	32.70%
Obligations of state and political subdivisions [Member] | Weighted Average [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)	8.40%	12.00%
Corporate securities [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Asset, fair value	$ 46	$ 56
Yield (as a percent)	35.80%	29.50%
RMBS [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Asset, fair value	$ 316	$ 309
RMBS [Member] | Minimum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)	3.50%	5.30%
RMBS [Member] | Maximum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)	6.10%	8.10%
RMBS [Member] | Weighted Average [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)	4.20%	6.30%
Life Insurance Transaction [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Asset, fair value	$ 339	$ 620
Yield (as a percent)	5.50%
Life Insurance Transaction [Member] | Minimum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)		6.50%
Life Insurance Transaction [Member] | Maximum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)		7.10%
Life Insurance Transaction [Member] | Weighted Average [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)		6.80%
Collateralized loan obligations (CLO) /TruPS [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Asset, fair value	$ 274	$ 274
Collateralized loan obligations (CLO) /TruPS [Member] | Minimum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)	2.50%	3.80%
Collateralized loan obligations (CLO) /TruPS [Member] | Maximum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)	5.10%	4.70%
Collateralized loan obligations (CLO) /TruPS [Member] | Weighted Average [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)	3.60%	4.30%
Other Asset Backed Securities [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Asset, fair value	$ 51	$ 53
Yield (as a percent)	9.90%	11.50%
FG VIEs and other [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Asset, fair value	$ 469	$ 569
FG VIEs and other [Member] | Minimum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)	3.30%	5.00%
FG VIEs and other [Member] | Maximum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)	8.30%	10.20%
FG VIEs and other [Member] | Weighted Average [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)	5.00%	7.10%
Other Assets [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Asset, fair value	$ 70	$ 74
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)	5.80%	6.60%
Other Assets [Member] | Maximum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)	6.50%	7.20%
Other Assets [Member] | Weighted Average [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Yield (as a percent)	6.20%	6.90%
Other invested assets [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Asset, fair value	$ 6	$ 7
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	1.40%	3.40%
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	16.90%	19.40%
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	6.00%	6.20%
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	0.70%	0.90%
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	18.40%	18.10%
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	8.80%	9.30%
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	6.90%	6.90%
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%	5.20%
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%	1.30%
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	25.70%	23.70%
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	4.70%	5.10%
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	85.70%	82.70%
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	60.00%	60.00%
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	77.60%	79.80%