Investments - Loans by Property Type (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Investment Holdings [Line Items]
Commercial mortgage loans	$ 4,774	$ 4,664
Retail
Investment Holdings [Line Items]
Commercial mortgage loans	1,228	1,198
Industrial
Investment Holdings [Line Items]
Commercial mortgage loans	1,212	1,216
Apartments
Investment Holdings [Line Items]
Commercial mortgage loans	1,246	1,185
Office
Investment Holdings [Line Items]
Commercial mortgage loans	722	697
Hotel/Motel
Investment Holdings [Line Items]
Commercial mortgage loans	127	127
Other
Investment Holdings [Line Items]
Commercial mortgage loans	195	197
Mixed Use
Investment Holdings [Line Items]
Commercial mortgage loans	44	44
Year of Origination 2020
Investment Holdings [Line Items]
Commercial mortgage loans	195	0
Year of Origination 2020 | Retail
Investment Holdings [Line Items]
Commercial mortgage loans	44	0
Year of Origination 2020 | Industrial
Investment Holdings [Line Items]
Commercial mortgage loans	8	0
Year of Origination 2020 | Apartments
Investment Holdings [Line Items]
Commercial mortgage loans	98	0
Year of Origination 2020 | Office
Investment Holdings [Line Items]
Commercial mortgage loans	45	0
Year of Origination 2020 | Hotel/Motel
Investment Holdings [Line Items]
Commercial mortgage loans	0	0
Year of Origination 2020 | Other
Investment Holdings [Line Items]
Commercial mortgage loans	0	0
Year of Origination 2020 | Mixed Use
Investment Holdings [Line Items]
Commercial mortgage loans	0	0
Year of Origination 2019
Investment Holdings [Line Items]
Commercial mortgage loans	510	522
Year of Origination 2019 | Retail
Investment Holdings [Line Items]
Commercial mortgage loans	33	33
Year of Origination 2019 | Industrial
Investment Holdings [Line Items]
Commercial mortgage loans	90	90
Year of Origination 2019 | Apartments
Investment Holdings [Line Items]
Commercial mortgage loans	286	299
Year of Origination 2019 | Office
Investment Holdings [Line Items]
Commercial mortgage loans	81	81
Year of Origination 2019 | Hotel/Motel
Investment Holdings [Line Items]
Commercial mortgage loans	20	19
Year of Origination 2019 | Other
Investment Holdings [Line Items]
Commercial mortgage loans	0	0
Year of Origination 2019 | Mixed Use
Investment Holdings [Line Items]
Commercial mortgage loans	0	0
Year of Origination 2018
Investment Holdings [Line Items]
Commercial mortgage loans	315	349
Year of Origination 2018 | Retail
Investment Holdings [Line Items]
Commercial mortgage loans	50	52
Year of Origination 2018 | Industrial
Investment Holdings [Line Items]
Commercial mortgage loans	90	91
Year of Origination 2018 | Apartments
Investment Holdings [Line Items]
Commercial mortgage loans	137	152
Year of Origination 2018 | Office
Investment Holdings [Line Items]
Commercial mortgage loans	17	32
Year of Origination 2018 | Hotel/Motel
Investment Holdings [Line Items]
Commercial mortgage loans	3	4
Year of Origination 2018 | Other
Investment Holdings [Line Items]
Commercial mortgage loans	18	18
Year of Origination 2018 | Mixed Use
Investment Holdings [Line Items]
Commercial mortgage loans	0	0
Year of Origination 2017
Investment Holdings [Line Items]
Commercial mortgage loans	926	934
Year of Origination 2017 | Retail
Investment Holdings [Line Items]
Commercial mortgage loans	103	104
Year of Origination 2017 | Industrial
Investment Holdings [Line Items]
Commercial mortgage loans	456	461
Year of Origination 2017 | Apartments
Investment Holdings [Line Items]
Commercial mortgage loans	218	218
Year of Origination 2017 | Office
Investment Holdings [Line Items]
Commercial mortgage loans	145	147
Year of Origination 2017 | Hotel/Motel
Investment Holdings [Line Items]
Commercial mortgage loans	4	4
Year of Origination 2017 | Other
Investment Holdings [Line Items]
Commercial mortgage loans	0	0
Year of Origination 2017 | Mixed Use
Investment Holdings [Line Items]
Commercial mortgage loans	0	0
Year of Origination 2016
Investment Holdings [Line Items]
Commercial mortgage loans	693	697
Year of Origination 2016 | Retail
Investment Holdings [Line Items]
Commercial mortgage loans	130	131
Year of Origination 2016 | Industrial
Investment Holdings [Line Items]
Commercial mortgage loans	251	254
Year of Origination 2016 | Apartments
Investment Holdings [Line Items]
Commercial mortgage loans	147	147
Year of Origination 2016 | Office
Investment Holdings [Line Items]
Commercial mortgage loans	146	146
Year of Origination 2016 | Hotel/Motel
Investment Holdings [Line Items]
Commercial mortgage loans	8	8
Year of Origination 2016 | Other
Investment Holdings [Line Items]
Commercial mortgage loans	7	7
Year of Origination 2016 | Mixed Use
Investment Holdings [Line Items]
Commercial mortgage loans	4	4
Year of Origination 2015
Investment Holdings [Line Items]
Commercial mortgage loans	526	529
Year of Origination 2015 | Retail
Investment Holdings [Line Items]
Commercial mortgage loans	147	148
Year of Origination 2015 | Industrial
Investment Holdings [Line Items]
Commercial mortgage loans	183	185
Year of Origination 2015 | Apartments
Investment Holdings [Line Items]
Commercial mortgage loans	68	69
Year of Origination 2015 | Office
Investment Holdings [Line Items]
Commercial mortgage loans	62	62
Year of Origination 2015 | Hotel/Motel
Investment Holdings [Line Items]
Commercial mortgage loans	24	23
Year of Origination 2015 | Other
Investment Holdings [Line Items]
Commercial mortgage loans	42	42
Year of Origination 2015 | Mixed Use
Investment Holdings [Line Items]
Commercial mortgage loans	0	0
Year of Origination 2014 and prior
Investment Holdings [Line Items]
Commercial mortgage loans	1,609	1,633
Year of Origination 2014 and prior | Retail
Investment Holdings [Line Items]
Commercial mortgage loans	721	730
Year of Origination 2014 and prior | Industrial
Investment Holdings [Line Items]
Commercial mortgage loans	134	135
Year of Origination 2014 and prior | Apartments
Investment Holdings [Line Items]
Commercial mortgage loans	292	300
Year of Origination 2014 and prior | Office
Investment Holdings [Line Items]
Commercial mortgage loans	226	229
Year of Origination 2014 and prior | Hotel/Motel
Investment Holdings [Line Items]
Commercial mortgage loans	68	69
Year of Origination 2014 and prior | Other
Investment Holdings [Line Items]
Commercial mortgage loans	128	130
Year of Origination 2014 and prior | Mixed Use
Investment Holdings [Line Items]
Commercial mortgage loans	$ 40	$ 40