Fair Value Measurements - Significant Unobservable Inputs - Securities (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total fixed maturities	$ 42,148	$ 35,652
CMBS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total fixed maturities	4,338	3,552
Corporate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total fixed maturities	17,396	13,398
Municipal
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total fixed maturities	9,498	10,346
Residential mortgage-backed securities (RMBS)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total fixed maturities	4,869	3,279
Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total fixed maturities	1,414	1,565
Significant Unobservable Inputs (Level 3) | CMBS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total fixed maturities	9	12
Significant Unobservable Inputs (Level 3) | Corporate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total fixed maturities	732	520
Significant Unobservable Inputs (Level 3) | Municipal
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total fixed maturities	0	0
Significant Unobservable Inputs (Level 3) | Residential mortgage-backed securities (RMBS)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total fixed maturities	560	920
Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring | CLOs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total fixed maturities	$ 95
Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring | CLOs | Measurement Input, Credit Spread [Member] | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Servicing Asset, Measurement Input	2.46
Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring | CLOs | Measurement Input, Credit Spread [Member] | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Servicing Asset, Measurement Input	2.46
Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring | CLOs | Measurement Input, Credit Spread [Member] | Weighted Average Expected Life
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Servicing Asset, Measurement Input	2.46
Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring | CMBS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total fixed maturities	$ 1	$ 2
Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring | CMBS | Measurement Input, Credit Spread [Member] | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Servicing Asset, Measurement Input	0.09	0.09
Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring | CMBS | Measurement Input, Credit Spread [Member] | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Servicing Asset, Measurement Input	18.32	10.40
Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring | CMBS | Measurement Input, Credit Spread [Member] | Weighted Average Expected Life
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Servicing Asset, Measurement Input	1.61	1.82
Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring | Corporate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total fixed maturities	$ 633	$ 274
Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring | Corporate | Measurement Input, Credit Spread [Member] | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Servicing Asset, Measurement Input	0.93	1.45
Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring | Corporate | Measurement Input, Credit Spread [Member] | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Servicing Asset, Measurement Input	7.88	11.75
Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring | Corporate | Measurement Input, Credit Spread [Member] | Weighted Average Expected Life
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Servicing Asset, Measurement Input	2.36	2.63
Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring | Residential mortgage-backed securities (RMBS)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total fixed maturities	$ 560	$ 815
Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring | Residential mortgage-backed securities (RMBS) | Measurement Input, Credit Spread [Member] | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Servicing Asset, Measurement Input	0.05	0.12
Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring | Residential mortgage-backed securities (RMBS) | Measurement Input, Credit Spread [Member] | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Servicing Asset, Measurement Input	2.33	2.15
Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring | Residential mortgage-backed securities (RMBS) | Measurement Input, Credit Spread [Member] | Weighted Average Expected Life
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Servicing Asset, Measurement Input	0.79	0.86
Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring | Residential mortgage-backed securities (RMBS) | Measurement Input, Constant Prepayment Rate [Member] | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Servicing Assets and Servicing Liabilities at Fair Value, Assumptions Used to Estimate Fair Value, Prepayment Speed	0.00%	1.00%
Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring | Residential mortgage-backed securities (RMBS) | Measurement Input, Constant Prepayment Rate [Member] | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Servicing Assets and Servicing Liabilities at Fair Value, Assumptions Used to Estimate Fair Value, Prepayment Speed	11.00%	15.00%
Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring | Residential mortgage-backed securities (RMBS) | Measurement Input, Constant Prepayment Rate [Member] | Weighted Average Expected Life
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Servicing Assets and Servicing Liabilities at Fair Value, Assumptions Used to Estimate Fair Value, Prepayment Speed	6.00%	6.00%
Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring | Residential mortgage-backed securities (RMBS) | Measurement Input, Default Rate [Member] | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Servicing Assets and Servicing Liabilities at Fair Value, Assumptions Used to Estimate Fair Value, Expected Credit Losses	1.00%	1.00%
Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring | Residential mortgage-backed securities (RMBS) | Measurement Input, Default Rate [Member] | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Servicing Assets and Servicing Liabilities at Fair Value, Assumptions Used to Estimate Fair Value, Expected Credit Losses	6.00%	8.00%
Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring | Residential mortgage-backed securities (RMBS) | Measurement Input, Default Rate [Member] | Weighted Average Expected Life
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Servicing Assets and Servicing Liabilities at Fair Value, Assumptions Used to Estimate Fair Value, Expected Credit Losses	3.00%	3.00%
Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring | Residential mortgage-backed securities (RMBS) | Measurement Input, Loss Severity [Member] | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Servicing Assets and Servicing Liabilities at Fair Value, Assumptions Used to Estimate Fair Value, Expected Credit Losses	0.00%	0.00%
Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring | Residential mortgage-backed securities (RMBS) | Measurement Input, Loss Severity [Member] | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Servicing Assets and Servicing Liabilities at Fair Value, Assumptions Used to Estimate Fair Value, Expected Credit Losses	100.00%	100.00%
Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring | Residential mortgage-backed securities (RMBS) | Measurement Input, Loss Severity [Member] | Weighted Average Expected Life
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Servicing Assets and Servicing Liabilities at Fair Value, Assumptions Used to Estimate Fair Value, Expected Credit Losses	70.00%	61.00%