Investments - Loans by Debt Service Coverage Ratio (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Commercial mortgage loans	$ 4,774	$ 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	$ 3,694	$ 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	$ 563	$ 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	$ 372	$ 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	$ 145	$ 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	195	0
Year of Origination 2020 | Greater than 1.5x
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Commercial mortgage loans	140	0
Year of Origination 2020 | 1.25x - 1.5x
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Commercial mortgage loans	31	0
Year of Origination 2020 | 1.0x - 1.25x
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Commercial mortgage loans	24	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	510	522
Year of Origination 2019 | Greater than 1.5x
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Commercial mortgage loans	392	353
Year of Origination 2019 | 1.25x - 1.5x
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Commercial mortgage loans	76	127
Year of Origination 2019 | 1.0x - 1.25x
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Commercial mortgage loans	42	42
Year of Origination 2019 | Less than 1.0x
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Commercial mortgage loans	0	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	315	349
Year of Origination 2018 | Greater than 1.5x
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Commercial mortgage loans	217	236
Year of Origination 2018 | 1.25x - 1.5x
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Commercial mortgage loans	3	3
Year of Origination 2018 | 1.0x - 1.25x
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Commercial mortgage loans	64	60
Year of Origination 2018 | Less than 1.0x
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Commercial mortgage loans	31	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	926	934
Year of Origination 2017 | Greater than 1.5x
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Commercial mortgage loans	491	481
Year of Origination 2017 | 1.25x - 1.5x
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Commercial mortgage loans	224	238
Year of Origination 2017 | 1.0x - 1.25x
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Commercial mortgage loans	143	133
Year of Origination 2017 | Less than 1.0x
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Commercial mortgage loans	68	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	693	697
Year of Origination 2016 | Greater than 1.5x
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Commercial mortgage loans	607	615
Year of Origination 2016 | 1.25x - 1.5x
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Commercial mortgage loans	63	59
Year of Origination 2016 | 1.0x - 1.25x
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Commercial mortgage loans	23	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	526	529
Year of Origination 2015 | Greater than 1.5x
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Commercial mortgage loans	494	492
Year of Origination 2015 | 1.25x - 1.5x
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Commercial mortgage loans	32	32
Year of Origination 2015 | 1.0x - 1.25x
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Commercial mortgage loans	0	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	1,609	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	1,353	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	134	128
Year of Origination 2014 and prior | 1.0x - 1.25x
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Commercial mortgage loans	76	88
Year of Origination 2014 and prior | Less than 1.0x
Schedule of Loans by Debt Service Coverage Ratio [Line Items]
Commercial mortgage loans	46	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