Investments - Schedule of Commercial Mortgage Loan Investment (Details) $ in Millions	Dec. 31, 2017 USD ($) loan	Sep. 30, 2018 USD ($)
Schedule of Investments [Line Items]
Impaired loans, number | loan	0
Commercial mortgage loans		$ 497
Commercial mortgage loans, % of total		100.00%
Loans and Leases Receivable, Net Amount	$ 548	$ 497
Funeral Home
Schedule of Investments [Line Items]
Commercial mortgage loans		$ 22
Commercial mortgage loans, % of total		4.00%
Hotel
Schedule of Investments [Line Items]
Commercial mortgage loans		$ 45
Commercial mortgage loans, % of total		9.00%
Industrial - General
Schedule of Investments [Line Items]
Commercial mortgage loans		$ 12
Commercial mortgage loans, % of total		2.00%
Industrial - Warehouse
Schedule of Investments [Line Items]
Commercial mortgage loans		$ 69
Commercial mortgage loans, % of total		14.00%
Multifamily
Schedule of Investments [Line Items]
Commercial mortgage loans		$ 147
Commercial mortgage loans, % of total		30.00%
Office
Schedule of Investments [Line Items]
Commercial mortgage loans		$ 202
Commercial mortgage loans, % of total		41.00%
Self Storage [Member]
Schedule of Investments [Line Items]
Commercial mortgage loans	$ 548	$ 497
Commercial mortgage loans, % of total	100.00%	100.00%
LTV Less Than 50 Percent
Schedule of Investments [Line Items]
Commercial mortgage loans		$ 256
Commercial mortgage loans, % of total		52.00%
LTV 50 to 60 Percent
Schedule of Investments [Line Items]
Commercial mortgage loans		$ 229
Commercial mortgage loans, % of total		46.00%
LTV 60 to 75 Percent
Schedule of Investments [Line Items]
Commercial mortgage loans		$ 12
Commercial mortgage loans, % of total		2.00%
East North Central
Schedule of Investments [Line Items]
Commercial mortgage loans		$ 111
Commercial mortgage loans, % of total		22.00%
East South Central
Schedule of Investments [Line Items]
Commercial mortgage loans		$ 20
Commercial mortgage loans, % of total		4.00%
Middle Atlantic
Schedule of Investments [Line Items]
Commercial mortgage loans		$ 79
Commercial mortgage loans, % of total		16.00%
Mountain
Schedule of Investments [Line Items]
Commercial mortgage loans		$ 65
Commercial mortgage loans, % of total		13.00%
New England
Schedule of Investments [Line Items]
Commercial mortgage loans		$ 10
Commercial mortgage loans, % of total		2.00%
Pacific
Schedule of Investments [Line Items]
Commercial mortgage loans		$ 116
Commercial mortgage loans, % of total		23.00%
South Atlantic
Schedule of Investments [Line Items]
Commercial mortgage loans		$ 58
Commercial mortgage loans, % of total		12.00%
West North Central
Schedule of Investments [Line Items]
Commercial mortgage loans		$ 13
Commercial mortgage loans, % of total		3.00%
West South Central
Schedule of Investments [Line Items]
Commercial mortgage loans		$ 25
Commercial mortgage loans, % of total		5.00%
Greater than 1.25
Schedule of Investments [Line Items]
Commercial mortgage loans		$ 490
Greater than 1.25 | LTV Less Than 50 Percent
Schedule of Investments [Line Items]
Commercial mortgage loans		256
Greater than 1.25 | LTV 50 to 60 Percent
Schedule of Investments [Line Items]
Commercial mortgage loans		222
Greater than 1.25 | LTV 60 to 75 Percent
Schedule of Investments [Line Items]
Commercial mortgage loans		12
Greater than 1.00 but less than 1.25
Schedule of Investments [Line Items]
Commercial mortgage loans		7
Greater than 1.00 but less than 1.25 | LTV Less Than 50 Percent
Schedule of Investments [Line Items]
Commercial mortgage loans		0
Greater than 1.00 but less than 1.25 | LTV 50 to 60 Percent
Schedule of Investments [Line Items]
Commercial mortgage loans		7
Greater than 1.00 but less than 1.25 | LTV 60 to 75 Percent
Schedule of Investments [Line Items]
Commercial mortgage loans		0
Fair Value
Schedule of Investments [Line Items]
Commercial mortgage loans		$ 488
Commercial mortgage loans, % of total		100.00%
Fair Value | LTV Less Than 50 Percent
Schedule of Investments [Line Items]
Commercial mortgage loans		$ 252
Commercial mortgage loans, % of total		52.00%
Fair Value | LTV 50 to 60 Percent
Schedule of Investments [Line Items]
Commercial mortgage loans		$ 225
Commercial mortgage loans, % of total		46.00%
Fair Value | LTV 60 to 75 Percent
Schedule of Investments [Line Items]
Commercial mortgage loans		$ 11
Commercial mortgage loans, % of total		2.00%
Commercial Portfolio Segment [Member]
Schedule of Investments [Line Items]
Commercial mortgage loans		$ 497
Commercial mortgage loans, % of total		100.00%
Allowance for loan loss		$ 0
Loans and Leases Receivable, Net Amount		$ 497
Predecessor
Schedule of Investments [Line Items]
Commercial mortgage loans	$ 548
Commercial mortgage loans, % of total	100.00%
Predecessor | Funeral Home
Schedule of Investments [Line Items]
Commercial mortgage loans	$ 22
Commercial mortgage loans, % of total	4.00%
Predecessor | Hotel
Schedule of Investments [Line Items]
Commercial mortgage loans	$ 46
Commercial mortgage loans, % of total	9.00%
Predecessor | Industrial - General
Schedule of Investments [Line Items]
Commercial mortgage loans	$ 38
Commercial mortgage loans, % of total	6.00%
Predecessor | Industrial - Warehouse
Schedule of Investments [Line Items]
Commercial mortgage loans	$ 70
Commercial mortgage loans, % of total	13.00%
Predecessor | Multifamily
Schedule of Investments [Line Items]
Commercial mortgage loans	$ 158
Commercial mortgage loans, % of total	29.00%
Predecessor | Office
Schedule of Investments [Line Items]
Commercial mortgage loans	$ 214
Commercial mortgage loans, % of total	39.00%
Predecessor | LTV Less Than 50 Percent
Schedule of Investments [Line Items]
Commercial mortgage loans	$ 293
Commercial mortgage loans, % of total	54.00%
Predecessor | LTV 50 to 60 Percent
Schedule of Investments [Line Items]
Commercial mortgage loans	$ 243
Commercial mortgage loans, % of total	44.00%
Predecessor | LTV 60 to 75 Percent
Schedule of Investments [Line Items]
Commercial mortgage loans	$ 12
Commercial mortgage loans, % of total	2.00%
Predecessor | East North Central
Schedule of Investments [Line Items]
Commercial mortgage loans	$ 108
Commercial mortgage loans, % of total	20.00%
Predecessor | East South Central
Schedule of Investments [Line Items]
Commercial mortgage loans	$ 20
Commercial mortgage loans, % of total	4.00%
Predecessor | Middle Atlantic
Schedule of Investments [Line Items]
Commercial mortgage loans	$ 85
Commercial mortgage loans, % of total	15.00%
Predecessor | Mountain
Schedule of Investments [Line Items]
Commercial mortgage loans	$ 67
Commercial mortgage loans, % of total	12.00%
Predecessor | New England
Schedule of Investments [Line Items]
Commercial mortgage loans	$ 14
Commercial mortgage loans, % of total	3.00%
Predecessor | Pacific
Schedule of Investments [Line Items]
Commercial mortgage loans	$ 135
Commercial mortgage loans, % of total	25.00%
Predecessor | South Atlantic
Schedule of Investments [Line Items]
Commercial mortgage loans	$ 65
Commercial mortgage loans, % of total	12.00%
Predecessor | West North Central
Schedule of Investments [Line Items]
Commercial mortgage loans	$ 13
Commercial mortgage loans, % of total	2.00%
Predecessor | West South Central
Schedule of Investments [Line Items]
Commercial mortgage loans	$ 41
Commercial mortgage loans, % of total	7.00%
Predecessor | Greater than 1.25
Schedule of Investments [Line Items]
Commercial mortgage loans	$ 541
Predecessor | Greater than 1.25 | LTV Less Than 50 Percent
Schedule of Investments [Line Items]
Commercial mortgage loans	293
Predecessor | Greater than 1.25 | LTV 50 to 60 Percent
Schedule of Investments [Line Items]
Commercial mortgage loans	236
Predecessor | Greater than 1.25 | LTV 60 to 75 Percent
Schedule of Investments [Line Items]
Commercial mortgage loans	12
Predecessor | Greater than 1.00 but less than 1.25
Schedule of Investments [Line Items]
Commercial mortgage loans	7
Predecessor | Greater than 1.00 but less than 1.25 | LTV Less Than 50 Percent
Schedule of Investments [Line Items]
Commercial mortgage loans	0
Predecessor | Greater than 1.00 but less than 1.25 | LTV 50 to 60 Percent
Schedule of Investments [Line Items]
Commercial mortgage loans	7
Predecessor | Greater than 1.00 but less than 1.25 | LTV 60 to 75 Percent
Schedule of Investments [Line Items]
Commercial mortgage loans	0
Predecessor | Fair Value
Schedule of Investments [Line Items]
Commercial mortgage loans	$ 549
Commercial mortgage loans, % of total	100.00%
Predecessor | Fair Value | LTV Less Than 50 Percent
Schedule of Investments [Line Items]
Commercial mortgage loans	$ 294
Commercial mortgage loans, % of total	54.00%
Predecessor | Fair Value | LTV 50 to 60 Percent
Schedule of Investments [Line Items]
Commercial mortgage loans	$ 243
Commercial mortgage loans, % of total	44.00%
Predecessor | Fair Value | LTV 60 to 75 Percent
Schedule of Investments [Line Items]
Commercial mortgage loans	$ 12
Commercial mortgage loans, % of total	2.00%
Predecessor | Commercial Portfolio Segment [Member]
Schedule of Investments [Line Items]
Commercial mortgage loans	$ 548
Commercial mortgage loans, % of total	100.00%
Allowance for loan loss	$ 0
Loans and Leases Receivable, Net Amount	$ 548