Investments - Unrealized Loss Position Maturities (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Less than one year	$ 16
One year through five years	61
After five years through ten years	128
Greater than ten years	49
Fair Value	600
Unrealized Losses
Less than one year	0
One year through five years	1
After five years through ten years	2
Greater than ten years	0
Unrealized Losses	7
Residential mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Debt securities, maturity, without single maturity date, fair value	2
Fair Value	2	$ 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	344
Fair Value	344	528
Unrealized Losses
Debt securities, maturity, without single maturity date, unrealized losses	4
Unrealized Losses	4	$ 15
Supporting experience-rated products
Debt Securities, Available-for-sale [Line Items]
Less than one year	0
One year through five years	0
After five years through ten years	3
Greater than ten years	3
Fair Value	6
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	0
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	16
One year through five years	61
After five years through ten years	125
Greater than ten years	46
Fair Value	594
Unrealized Losses
Less than one year	0
One year through five years	1
After five years through ten years	2
Greater than ten years	0
Unrealized Losses	7
Supporting remaining products | Residential mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Debt securities, maturity, without single maturity date, fair value	2
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	344
Unrealized Losses
Debt securities, maturity, without single maturity date, unrealized losses	$ 4