Investments - Loans by U.S. Region (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Open Option Contracts Written [Line Items]
Commercial mortgage loans	$ 4,731	$ 4,664
Pacific
Open Option Contracts Written [Line Items]
Commercial mortgage loans	969	944
South Atlantic
Open Option Contracts Written [Line Items]
Commercial mortgage loans	1,034	966
Middle Atlantic
Open Option Contracts Written [Line Items]
Commercial mortgage loans	977	1,019
West South Central
Open Option Contracts Written [Line Items]
Commercial mortgage loans	543	537
Mountain
Open Option Contracts Written [Line Items]
Commercial mortgage loans	451	442
East North Central
Open Option Contracts Written [Line Items]
Commercial mortgage loans	385	383
New England
Open Option Contracts Written [Line Items]
Commercial mortgage loans	82	84
West North Central
Open Option Contracts Written [Line Items]
Commercial mortgage loans	210	212
East South Central
Open Option Contracts Written [Line Items]
Commercial mortgage loans	80	77
Year of Origination 2020
Open Option Contracts Written [Line Items]
Commercial mortgage loans	257	0
Year of Origination 2020 | Pacific
Open Option Contracts Written [Line Items]
Commercial mortgage loans	56	0
Year of Origination 2020 | South Atlantic
Open Option Contracts Written [Line Items]
Commercial mortgage loans	121	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	18	0
Year of Origination 2019
Open Option Contracts Written [Line Items]
Commercial mortgage loans	513	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	129	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	156	155
Year of Origination 2019 | Mountain
Open Option Contracts Written [Line Items]
Commercial mortgage loans	54	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	305	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	59	60
Year of Origination 2018 | West South Central
Open Option Contracts Written [Line Items]
Commercial mortgage loans	35	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	895	934
Year of Origination 2017 | Pacific
Open Option Contracts Written [Line Items]
Commercial mortgage loans	101	103
Year of Origination 2017 | South Atlantic
Open Option Contracts Written [Line Items]
Commercial mortgage loans	98	99
Year of Origination 2017 | Middle Atlantic
Open Option Contracts Written [Line Items]
Commercial mortgage loans	362	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	76	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	688	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	131	132
Year of Origination 2016 | Middle Atlantic
Open Option Contracts Written [Line Items]
Commercial mortgage loans	183	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	73	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	8	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	483	529
Year of Origination 2015 | Pacific
Open Option Contracts Written [Line Items]
Commercial mortgage loans	111	125
Year of Origination 2015 | South Atlantic
Open Option Contracts Written [Line Items]
Commercial mortgage loans	135	160
Year of Origination 2015 | Middle Atlantic
Open Option Contracts Written [Line Items]
Commercial mortgage loans	101	103
Year of Origination 2015 | West South Central
Open Option Contracts Written [Line Items]
Commercial mortgage loans	31	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	48	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	5	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	1,590	1,633
Year of Origination 2014 and prior | Pacific
Open Option Contracts Written [Line Items]
Commercial mortgage loans	431	445
Year of Origination 2014 and prior | South Atlantic
Open Option Contracts Written [Line Items]
Commercial mortgage loans	308	316
Year of Origination 2014 and prior | Middle Atlantic
Open Option Contracts Written [Line Items]
Commercial mortgage loans	244	247
Year of Origination 2014 and prior | West South Central
Open Option Contracts Written [Line Items]
Commercial mortgage loans	116	122
Year of Origination 2014 and prior | Mountain
Open Option Contracts Written [Line Items]
Commercial mortgage loans	166	168
Year of Origination 2014 and prior | East North Central
Open Option Contracts Written [Line Items]
Commercial mortgage loans	137	142
Year of Origination 2014 and prior | New England
Open Option Contracts Written [Line Items]
Commercial mortgage loans	41	42
Year of Origination 2014 and prior | West North Central
Open Option Contracts Written [Line Items]
Commercial mortgage loans	117	121
Year of Origination 2014 and prior | East South Central
Open Option Contracts Written [Line Items]
Commercial mortgage loans	$ 30	$ 30