Investments - Net Investment Income (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Schedule of Investments [Line Items]
Gross investment income	$ 289		$ 860
Investment expense	(22)		(48)
Net investment income	267		812
Fixed maturity securities, available-for-sale
Schedule of Investments [Line Items]
Gross investment income	249		739
Equity securities
Schedule of Investments [Line Items]
Gross investment income	15		51
Commercial mortgage loans
Schedule of Investments [Line Items]
Gross investment income	5		17
Related Party Loans [Member]
Schedule of Investments [Line Items]
Gross investment income	1		1
Invested cash and short-term investments
Schedule of Investments [Line Items]
Gross investment income	6		13
Other investments
Schedule of Investments [Line Items]
Gross investment income	$ 13		$ 39
Predecessor
Schedule of Investments [Line Items]
Gross investment income		$ 266		$ 782
Investment expense		(5)		(17)
Net investment income		261		765
Predecessor | Fixed maturity securities, available-for-sale
Schedule of Investments [Line Items]
Gross investment income		247		725
Predecessor | Equity securities
Schedule of Investments [Line Items]
Gross investment income		10		31
Predecessor | Commercial mortgage loans
Schedule of Investments [Line Items]
Gross investment income		5		17
Predecessor | Related Party Loans [Member]
Schedule of Investments [Line Items]
Gross investment income		0		0
Predecessor | Invested cash and short-term investments
Schedule of Investments [Line Items]
Gross investment income		1		3
Predecessor | Other investments
Schedule of Investments [Line Items]
Gross investment income		$ 3		$ 6