Investments - Loans by U.S. Region (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Open Option Contracts Written [Line Items]
Commercial mortgage loans	$ 4,774	$ 4,664
Pacific
Open Option Contracts Written [Line Items]
Commercial mortgage loans	946	944
South Atlantic
Open Option Contracts Written [Line Items]
Commercial mortgage loans	1,052	966
Middle Atlantic
Open Option Contracts Written [Line Items]
Commercial mortgage loans	1,012	1,019
West South Central
Open Option Contracts Written [Line Items]
Commercial mortgage loans	556	537
Mountain
Open Option Contracts Written [Line Items]
Commercial mortgage loans	453	442
East North Central
Open Option Contracts Written [Line Items]
Commercial mortgage loans	390	383
New England
Open Option Contracts Written [Line Items]
Commercial mortgage loans	84	84
West North Central
Open Option Contracts Written [Line Items]
Commercial mortgage loans	211	212
East South Central
Open Option Contracts Written [Line Items]
Commercial mortgage loans	70	77
Year of Origination 2020
Open Option Contracts Written [Line Items]
Commercial mortgage loans	195	0
Year of Origination 2020 | Pacific
Open Option Contracts Written [Line Items]
Commercial mortgage loans	14	0
Year of Origination 2020 | South Atlantic
Open Option Contracts Written [Line Items]
Commercial mortgage loans	111	0
Year of Origination 2020 | Middle Atlantic
Open Option Contracts Written [Line Items]
Commercial mortgage loans	17	0
Year of Origination 2020 | West South Central
Open Option Contracts Written [Line Items]
Commercial mortgage loans	23	0
Year of Origination 2020 | Mountain
Open Option Contracts Written [Line Items]
Commercial mortgage loans	14	0
Year of Origination 2020 | East North Central
Open Option Contracts Written [Line Items]
Commercial mortgage loans	8	0
Year of Origination 2020 | New England
Open Option Contracts Written [Line Items]
Commercial mortgage loans	0	0
Year of Origination 2020 | West North Central
Open Option Contracts Written [Line Items]
Commercial mortgage loans	0	0
Year of Origination 2020 | East South Central
Open Option Contracts Written [Line Items]
Commercial mortgage loans	8	0
Year of Origination 2019
Open Option Contracts Written [Line Items]
Commercial mortgage loans	510	522
Year of Origination 2019 | Pacific
Open Option Contracts Written [Line Items]
Commercial mortgage loans	64	63
Year of Origination 2019 | South Atlantic
Open Option Contracts Written [Line Items]
Commercial mortgage loans	128	127
Year of Origination 2019 | Middle Atlantic
Open Option Contracts Written [Line Items]
Commercial mortgage loans	11	26
Year of Origination 2019 | West South Central
Open Option Contracts Written [Line Items]
Commercial mortgage loans	155	155
Year of Origination 2019 | Mountain
Open Option Contracts Written [Line Items]
Commercial mortgage loans	53	53
Year of Origination 2019 | East North Central
Open Option Contracts Written [Line Items]
Commercial mortgage loans	44	43
Year of Origination 2019 | New England
Open Option Contracts Written [Line Items]
Commercial mortgage loans	18	18
Year of Origination 2019 | West North Central
Open Option Contracts Written [Line Items]
Commercial mortgage loans	11	11
Year of Origination 2019 | East South Central
Open Option Contracts Written [Line Items]
Commercial mortgage loans	26	26
Year of Origination 2018
Open Option Contracts Written [Line Items]
Commercial mortgage loans	315	349
Year of Origination 2018 | Pacific
Open Option Contracts Written [Line Items]
Commercial mortgage loans	49	50
Year of Origination 2018 | South Atlantic
Open Option Contracts Written [Line Items]
Commercial mortgage loans	112	132
Year of Origination 2018 | Middle Atlantic
Open Option Contracts Written [Line Items]
Commercial mortgage loans	60	60
Year of Origination 2018 | West South Central
Open Option Contracts Written [Line Items]
Commercial mortgage loans	44	43
Year of Origination 2018 | Mountain
Open Option Contracts Written [Line Items]
Commercial mortgage loans	26	26
Year of Origination 2018 | East North Central
Open Option Contracts Written [Line Items]
Commercial mortgage loans	11	11
Year of Origination 2018 | New England
Open Option Contracts Written [Line Items]
Commercial mortgage loans	0	0
Year of Origination 2018 | West North Central
Open Option Contracts Written [Line Items]
Commercial mortgage loans	13	12
Year of Origination 2018 | East South Central
Open Option Contracts Written [Line Items]
Commercial mortgage loans	0	15
Year of Origination 2017
Open Option Contracts Written [Line Items]
Commercial mortgage loans	926	934
Year of Origination 2017 | Pacific
Open Option Contracts Written [Line Items]
Commercial mortgage loans	102	103
Year of Origination 2017 | South Atlantic
Open Option Contracts Written [Line Items]
Commercial mortgage loans	99	99
Year of Origination 2017 | Middle Atlantic
Open Option Contracts Written [Line Items]
Commercial mortgage loans	390	396
Year of Origination 2017 | West South Central
Open Option Contracts Written [Line Items]
Commercial mortgage loans	150	151
Year of Origination 2017 | Mountain
Open Option Contracts Written [Line Items]
Commercial mortgage loans	77	77
Year of Origination 2017 | East North Central
Open Option Contracts Written [Line Items]
Commercial mortgage loans	60	60
Year of Origination 2017 | New England
Open Option Contracts Written [Line Items]
Commercial mortgage loans	5	5
Year of Origination 2017 | West North Central
Open Option Contracts Written [Line Items]
Commercial mortgage loans	43	43
Year of Origination 2017 | East South Central
Open Option Contracts Written [Line Items]
Commercial mortgage loans	0	0
Year of Origination 2016
Open Option Contracts Written [Line Items]
Commercial mortgage loans	693	697
Year of Origination 2016 | Pacific
Open Option Contracts Written [Line Items]
Commercial mortgage loans	157	158
Year of Origination 2016 | South Atlantic
Open Option Contracts Written [Line Items]
Commercial mortgage loans	132	132
Year of Origination 2016 | Middle Atlantic
Open Option Contracts Written [Line Items]
Commercial mortgage loans	185	187
Year of Origination 2016 | West South Central
Open Option Contracts Written [Line Items]
Commercial mortgage loans	32	32
Year of Origination 2016 | Mountain
Open Option Contracts Written [Line Items]
Commercial mortgage loans	74	75
Year of Origination 2016 | East North Central
Open Option Contracts Written [Line Items]
Commercial mortgage loans	77	77
Year of Origination 2016 | New England
Open Option Contracts Written [Line Items]
Commercial mortgage loans	9	9
Year of Origination 2016 | West North Central
Open Option Contracts Written [Line Items]
Commercial mortgage loans	21	21
Year of Origination 2016 | East South Central
Open Option Contracts Written [Line Items]
Commercial mortgage loans	6	6
Year of Origination 2015
Open Option Contracts Written [Line Items]
Commercial mortgage loans	526	529
Year of Origination 2015 | Pacific
Open Option Contracts Written [Line Items]
Commercial mortgage loans	123	125
Year of Origination 2015 | South Atlantic
Open Option Contracts Written [Line Items]
Commercial mortgage loans	159	160
Year of Origination 2015 | Middle Atlantic
Open Option Contracts Written [Line Items]
Commercial mortgage loans	103	103
Year of Origination 2015 | West South Central
Open Option Contracts Written [Line Items]
Commercial mortgage loans	34	34
Year of Origination 2015 | Mountain
Open Option Contracts Written [Line Items]
Commercial mortgage loans	42	43
Year of Origination 2015 | East North Central
Open Option Contracts Written [Line Items]
Commercial mortgage loans	51	50
Year of Origination 2015 | New England
Open Option Contracts Written [Line Items]
Commercial mortgage loans	10	10
Year of Origination 2015 | West North Central
Open Option Contracts Written [Line Items]
Commercial mortgage loans	4	4
Year of Origination 2015 | East South Central
Open Option Contracts Written [Line Items]
Commercial mortgage loans	0	0
Year of Origination 2014 and prior
Open Option Contracts Written [Line Items]
Commercial mortgage loans	1,609	1,633
Year of Origination 2014 and prior | Pacific
Open Option Contracts Written [Line Items]
Commercial mortgage loans	437	445
Year of Origination 2014 and prior | South Atlantic
Open Option Contracts Written [Line Items]
Commercial mortgage loans	311	316
Year of Origination 2014 and prior | Middle Atlantic
Open Option Contracts Written [Line Items]
Commercial mortgage loans	246	247
Year of Origination 2014 and prior | West South Central
Open Option Contracts Written [Line Items]
Commercial mortgage loans	118	122
Year of Origination 2014 and prior | Mountain
Open Option Contracts Written [Line Items]
Commercial mortgage loans	167	168
Year of Origination 2014 and prior | East North Central
Open Option Contracts Written [Line Items]
Commercial mortgage loans	139	142
Year of Origination 2014 and prior | New England
Open Option Contracts Written [Line Items]
Commercial mortgage loans	42	42
Year of Origination 2014 and prior | West North Central
Open Option Contracts Written [Line Items]
Commercial mortgage loans	119	121
Year of Origination 2014 and prior | East South Central
Open Option Contracts Written [Line Items]
Commercial mortgage loans	$ 30	$ 30