Investments - Unrealized Loss Position Maturities (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Less than one year	$ 3
One year through five years	138
After five years through ten years	136
Greater than ten years	110
Fair Value	790	$ 2,409
Unrealized Losses
Less than one year	0
One year through five years	2
After five years through ten years	4
Greater than ten years	2
Unrealized Losses	13	36
Residential mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Debt securities, maturity, without single maturity date, fair value	17
Fair Value	17	1
Unrealized Losses
Debt securities, maturity, without single maturity date, unrealized losses	0
Unrealized Losses	0	0
Other asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Debt securities, maturity, without single maturity date, fair value	386
Fair Value	386	528
Unrealized Losses
Debt securities, maturity, without single maturity date, unrealized losses	5
Unrealized Losses	5	$ 15
Supporting experience-rated products
Debt Securities, Available-for-sale [Line Items]
Less than one year	0
One year through five years	1
After five years through ten years	8
Greater than ten years	11
Fair Value	30
Unrealized Losses
Less than one year	0
One year through five years	0
After five years through ten years	0
Greater than ten years	0
Unrealized Losses	0
Supporting experience-rated products | Residential mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Debt securities, maturity, without single maturity date, fair value	0
Unrealized Losses
Debt securities, maturity, without single maturity date, unrealized losses	0
Supporting experience-rated products | Other asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Debt securities, maturity, without single maturity date, fair value	10
Unrealized Losses
Debt securities, maturity, without single maturity date, unrealized losses	0
Supporting remaining products
Debt Securities, Available-for-sale [Line Items]
Less than one year	3
One year through five years	137
After five years through ten years	128
Greater than ten years	99
Fair Value	760
Unrealized Losses
Less than one year	0
One year through five years	2
After five years through ten years	4
Greater than ten years	2
Unrealized Losses	13
Supporting remaining products | Residential mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Debt securities, maturity, without single maturity date, fair value	17
Unrealized Losses
Debt securities, maturity, without single maturity date, unrealized losses	0
Supporting remaining products | Other asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Debt securities, maturity, without single maturity date, fair value	376
Unrealized Losses
Debt securities, maturity, without single maturity date, unrealized losses	$ 5