Investments - Loans by U.S. Region (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Open Option Contracts Written [Line Items]
Commercial mortgage loans	$ 4,670	$ 4,664
Pacific
Open Option Contracts Written [Line Items]
Commercial mortgage loans	967	944
South Atlantic
Open Option Contracts Written [Line Items]
Commercial mortgage loans	1,010	966
Middle Atlantic
Open Option Contracts Written [Line Items]
Commercial mortgage loans	962	1,019
West South Central
Open Option Contracts Written [Line Items]
Commercial mortgage loans	538	537
Mountain
Open Option Contracts Written [Line Items]
Commercial mortgage loans	449	442
East North Central
Open Option Contracts Written [Line Items]
Commercial mortgage loans	383	383
New England
Open Option Contracts Written [Line Items]
Commercial mortgage loans	80	84
West North Central
Open Option Contracts Written [Line Items]
Commercial mortgage loans	199	212
East South Central
Open Option Contracts Written [Line Items]
Commercial mortgage loans	82	77
Year of Origination 2020
Open Option Contracts Written [Line Items]
Commercial mortgage loans	282	0
Year of Origination 2020 | Pacific
Open Option Contracts Written [Line Items]
Commercial mortgage loans	62	0
Year of Origination 2020 | South Atlantic
Open Option Contracts Written [Line Items]
Commercial mortgage loans	124	0
Year of Origination 2020 | Middle Atlantic
Open Option Contracts Written [Line Items]
Commercial mortgage loans	20	0
Year of Origination 2020 | West South Central
Open Option Contracts Written [Line Items]
Commercial mortgage loans	28	0
Year of Origination 2020 | Mountain
Open Option Contracts Written [Line Items]
Commercial mortgage loans	15	0
Year of Origination 2020 | East North Central
Open Option Contracts Written [Line Items]
Commercial mortgage loans	13	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	20	0
Year of Origination 2019
Open Option Contracts Written [Line Items]
Commercial mortgage loans	496	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	125	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	149	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	38	43
Year of Origination 2019 | New England
Open Option Contracts Written [Line Items]
Commercial mortgage loans	17	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	27	26
Year of Origination 2018
Open Option Contracts Written [Line Items]
Commercial mortgage loans	290	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	99	132
Year of Origination 2018 | Middle Atlantic
Open Option Contracts Written [Line Items]
Commercial mortgage loans	57	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	881	934
Year of Origination 2017 | Pacific
Open Option Contracts Written [Line Items]
Commercial mortgage loans	100	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	357	396
Year of Origination 2017 | West South Central
Open Option Contracts Written [Line Items]
Commercial mortgage loans	149	151
Year of Origination 2017 | Mountain
Open Option Contracts Written [Line Items]
Commercial mortgage loans	75	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	37	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	684	697
Year of Origination 2016 | Pacific
Open Option Contracts Written [Line Items]
Commercial mortgage loans	156	158
Year of Origination 2016 | South Atlantic
Open Option Contracts Written [Line Items]
Commercial mortgage loans	130	132
Year of Origination 2016 | Middle Atlantic
Open Option Contracts Written [Line Items]
Commercial mortgage loans	180	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	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	479	529
Year of Origination 2015 | Pacific
Open Option Contracts Written [Line Items]
Commercial mortgage loans	110	125
Year of Origination 2015 | South Atlantic
Open Option Contracts Written [Line Items]
Commercial mortgage loans	134	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	9	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	1,558	1,633
Year of Origination 2014 and prior | Pacific
Open Option Contracts Written [Line Items]
Commercial mortgage loans	426	445
Year of Origination 2014 and prior | South Atlantic
Open Option Contracts Written [Line Items]
Commercial mortgage loans	300	316
Year of Origination 2014 and prior | Middle Atlantic
Open Option Contracts Written [Line Items]
Commercial mortgage loans	236	247
Year of Origination 2014 and prior | West South Central
Open Option Contracts Written [Line Items]
Commercial mortgage loans	114	122
Year of Origination 2014 and prior | Mountain
Open Option Contracts Written [Line Items]
Commercial mortgage loans	164	168
Year of Origination 2014 and prior | East North Central
Open Option Contracts Written [Line Items]
Commercial mortgage loans	136	142
Year of Origination 2014 and prior | New England
Open Option Contracts Written [Line Items]
Commercial mortgage loans	40	42
Year of Origination 2014 and prior | West North Central
Open Option Contracts Written [Line Items]
Commercial mortgage loans	113	121
Year of Origination 2014 and prior | East South Central
Open Option Contracts Written [Line Items]
Commercial mortgage loans	$ 29	$ 30