Related Party Transactions - Narrative (Details) shares in Thousands			1 Months Ended	3 Months Ended		9 Months Ended
	Sep. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2018 USD ($) shares	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) shares	Sep. 30, 2017 USD ($)
Related Party Transaction [Line Items]
Related Party Transactions, Gain (Loss)				$ 0	$ (1,000,000)		$ (3,000,000)
Payments for Merger Related Costs			$ 23,000,000
Management Fee Forgone				0.00%
Management Fee Forgone, Period				13 years
Management Fee Payable	$ 14,000,000			$ 14,000,000		$ 14,000,000
Related Party Transaction, Asset Carrying Value	445,000,000	$ 188,000,000	$ 188,000,000	445,000,000		445,000,000
Unrealized Loss on Foreign Currency Derivatives, before Tax	(1,000,000)	$ 0
Subsidiary of Common Parent [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Premiums Earned, Net, with Related Party				0
Benefits and other changes in policy reserves						0
Subsidiary of Common Parent [Member] | Predecessor
Related Party Transaction [Line Items]
Related Party Transaction, Premiums Earned, Net, with Related Party					0		1,000,000
Benefits and other changes in policy reserves					$ 12,000,000		$ 37,000,000
Commitment to Invest
Related Party Transaction [Line Items]
Unfunded investment commitment	$ 942,000,000			$ 942,000,000		$ 942,000,000
Commitment to Invest | Affiliated Entity
Related Party Transaction [Line Items]
Other Commitment, Number of Commitments	11			11		11
Unfunded investment commitment	$ 717,000,000			$ 717,000,000		$ 717,000,000
Preferred Stock | Affiliated Entity
Related Party Transaction [Line Items]
Total shares paid in kind (in thousands) | shares				5		15