Fair Value Measurements - Level 3 Financial Assets and Liabilities (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Percent of debt and equity securities classified in Level 3	2.00%
Fair Value, Measurements, Recurring [Member] | Fair Value Inputs Level 3 [Member] | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Debt securities	$ 399	$ 378
Fair Value, Measurements, Recurring [Member] | Fair Value Inputs Level 3 [Member] | Debt Securities [Member] | Securities not priced by the Company [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Debt securities	0	11
Fair Value, Measurements, Recurring [Member] | Fair Value Inputs Level 3 [Member] | Corporate and government fixed maturities [Member] | Unobservable Inputs Developed By Company [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Debt securities	$ 259	$ 229
Fair Value, Measurements, Recurring [Member] | Fair Value Inputs Level 3 [Member] | Corporate and government fixed maturities [Member] | Maximum [Member] | Unobservable Inputs Developed By Company [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Unobservable adjustment, liquidity	9.30%	9.30%
Fair Value, Measurements, Recurring [Member] | Fair Value Inputs Level 3 [Member] | Corporate and government fixed maturities [Member] | Minimum [Member] | Unobservable Inputs Developed By Company [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Unobservable adjustment, liquidity	0.70%	0.50%
Fair Value, Measurements, Recurring [Member] | Fair Value Inputs Level 3 [Member] | Corporate and government fixed maturities [Member] | Weighted Average [Member] | Unobservable Inputs Developed By Company [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Unobservable adjustment, liquidity	2.70%	2.30%
Fair Value, Measurements, Recurring [Member] | Fair Value Inputs Level 3 [Member] | Mortgage and other asset-backed securities [Member] | Unobservable Inputs Developed By Company [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Debt securities	$ 140	$ 138
Fair Value, Measurements, Recurring [Member] | Fair Value Inputs Level 3 [Member] | Mortgage and other asset-backed securities [Member] | Maximum [Member] | Unobservable Inputs Developed By Company [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Unobservable adjustment, liquidity	3.50%	3.40%
Unobservable adjustment, weighting of credit spreads	4.20%	3.40%
Fair Value, Measurements, Recurring [Member] | Fair Value Inputs Level 3 [Member] | Mortgage and other asset-backed securities [Member] | Minimum [Member] | Unobservable Inputs Developed By Company [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Unobservable adjustment, liquidity	0.60%	0.60%
Unobservable adjustment, weighting of credit spreads	2.30%	1.90%
Fair Value, Measurements, Recurring [Member] | Fair Value Inputs Level 3 [Member] | Mortgage and other asset-backed securities [Member] | Weighted Average [Member] | Unobservable Inputs Developed By Company [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Unobservable adjustment, liquidity	0.70%	0.70%
Unobservable adjustment, weighting of credit spreads	3.10%	2.60%