Investments - Loans by Debt Service Coverage Ratio (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Mar. 31, 2020	Sep. 30, 2020	Dec. 31, 2019
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Commercial mortgage loans		$ 4,670	$ 4,664
Loans and Leases Receivable, Debt Service Coverage, Benchmark Ratio	100.00%	100.00%
Greater than 1.5x
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Loans Receivable, Debt Service Coverage Ratio, Minimum	150.00%	150.00%
Commercial mortgage loans		$ 3,503	3,535
1.25x - 1.5x
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Loans Receivable, Debt Service Coverage Ratio, Minimum	125.00%	125.00%
Loans Receivable, Debt Service Coverage Ratio, Maximum	150.00%	150.00%
Commercial mortgage loans		$ 635	587
1.0x - 1.25x
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Loans Receivable, Debt Service Coverage Ratio, Minimum	100.00%	100.00%
Loans Receivable, Debt Service Coverage Ratio, Maximum	125.00%	125.00%
Commercial mortgage loans		$ 305	346
Less than 1.0x
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Loans Receivable, Debt Service Coverage Ratio, Minimum	0.00%	0.00%
Loans Receivable, Debt Service Coverage Ratio, Maximum	100.00%	100.00%
Commercial mortgage loans		$ 227	196
Commercial mortgage loans secured by land or construction loans
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Commercial mortgage loans		0	0
Year of Origination 2020
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Commercial mortgage loans		282	0
Year of Origination 2020 | Greater than 1.5x
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Commercial mortgage loans		218	0
Year of Origination 2020 | 1.25x - 1.5x
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Commercial mortgage loans		54	0
Year of Origination 2020 | 1.0x - 1.25x
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Commercial mortgage loans		10	0
Year of Origination 2020 | Less than 1.0x
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Commercial mortgage loans		0	0
Year of Origination 2020 | Commercial mortgage loans secured by land or construction loans
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Commercial mortgage loans		0	0
Year of Origination 2019
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Commercial mortgage loans		496	522
Year of Origination 2019 | Greater than 1.5x
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Commercial mortgage loans		328	353
Year of Origination 2019 | 1.25x - 1.5x
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Commercial mortgage loans		77	127
Year of Origination 2019 | 1.0x - 1.25x
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Commercial mortgage loans		36	42
Year of Origination 2019 | Less than 1.0x
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Commercial mortgage loans		55	0
Year of Origination 2019 | Commercial mortgage loans secured by land or construction loans
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Commercial mortgage loans		0	0
Year of Origination 2018
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Commercial mortgage loans		290	349
Year of Origination 2018 | Greater than 1.5x
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Commercial mortgage loans		129	236
Year of Origination 2018 | 1.25x - 1.5x
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Commercial mortgage loans		49	3
Year of Origination 2018 | 1.0x - 1.25x
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Commercial mortgage loans		65	60
Year of Origination 2018 | Less than 1.0x
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Commercial mortgage loans		47	50
Year of Origination 2018 | Commercial mortgage loans secured by land or construction loans
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Commercial mortgage loans		0	0
Year of Origination 2017
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Commercial mortgage loans		881	934
Year of Origination 2017 | Greater than 1.5x
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Commercial mortgage loans		496	481
Year of Origination 2017 | 1.25x - 1.5x
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Commercial mortgage loans		219	238
Year of Origination 2017 | 1.0x - 1.25x
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Commercial mortgage loans		105	133
Year of Origination 2017 | Less than 1.0x
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Commercial mortgage loans		61	82
Year of Origination 2017 | Commercial mortgage loans secured by land or construction loans
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Commercial mortgage loans		0	0
Year of Origination 2016
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Commercial mortgage loans		684	697
Year of Origination 2016 | Greater than 1.5x
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Commercial mortgage loans		598	615
Year of Origination 2016 | 1.25x - 1.5x
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Commercial mortgage loans		55	59
Year of Origination 2016 | 1.0x - 1.25x
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Commercial mortgage loans		31	23
Year of Origination 2016 | Less than 1.0x
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Commercial mortgage loans		0	0
Year of Origination 2016 | Commercial mortgage loans secured by land or construction loans
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Commercial mortgage loans		0	0
Year of Origination 2015
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Commercial mortgage loans		479	529
Year of Origination 2015 | Greater than 1.5x
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Commercial mortgage loans		455	492
Year of Origination 2015 | 1.25x - 1.5x
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Commercial mortgage loans		23	32
Year of Origination 2015 | 1.0x - 1.25x
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Commercial mortgage loans		1	0
Year of Origination 2015 | Less than 1.0x
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Commercial mortgage loans		0	5
Year of Origination 2015 | Commercial mortgage loans secured by land or construction loans
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Commercial mortgage loans		0	0
Year of Origination 2014 and prior
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Commercial mortgage loans		1,558	1,633
Year of Origination 2014 and prior | Greater than 1.5x
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Commercial mortgage loans		1,279	1,358
Year of Origination 2014 and prior | 1.25x - 1.5x
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Commercial mortgage loans		158	128
Year of Origination 2014 and prior | 1.0x - 1.25x
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Commercial mortgage loans		57	88
Year of Origination 2014 and prior | Less than 1.0x
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Commercial mortgage loans		64	59
Year of Origination 2014 and prior | Commercial mortgage loans secured by land or construction loans
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Commercial mortgage loans		$ 0	$ 0