Investments (Summary of available-for-sale other asset-backed securities in gross unrealized loss position by collateral and rating) (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	$ 10,153	$ 2,420
Gross Unrealized Losses	1,117	45
Other asset-backed
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	1,519	482
Gross Unrealized Losses	133	$ 4
Auto | Other asset-backed
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	290
Gross Unrealized Losses	6
Collateralized loan obligations | Other asset-backed
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	418
Gross Unrealized Losses	60
Franchise | Other asset-backed
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	414
Gross Unrealized Losses	39
Other | Other asset-backed
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	397
Gross Unrealized Losses	28
AAA | Other asset-backed
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	49
Gross Unrealized Losses	1
AA | Other asset-backed
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	83
Gross Unrealized Losses	2
A | Other asset-backed
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	821
Gross Unrealized Losses	74
BBB | Other asset-backed
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	566
Gross Unrealized Losses	56
Below investment grade | Other asset-backed
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	0
Gross Unrealized Losses	$ 0