Investments - Unrealized Capital Losses (Details) $ in Millions	Mar. 31, 2022 USD ($) securities	Dec. 31, 2021 USD ($) securities
Available-for-sale Securities Including Securities Pledged [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Number of Positions | securities	2,036	989
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	$ 674	$ 111
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	$ 538	$ 72
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions | securities	2,481	1,326
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Number of Positions | securities	445	337
Debt Securities, Available-for-sale, Unrealized Loss Position	$ 1,144	$ 708
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	9,317	3,838
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	136	39
Debt Securities, Available-for-sale, Unrealized Loss Position, Fair Value	$ 10,461	$ 4,546
U.S. Treasuries
Available-for-sale Securities Including Securities Pledged [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Number of Positions | securities	13	4
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	$ 7	$ 0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	$ 7	$ 0
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions | securities	16	6
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Number of Positions | securities	3	2
Debt Securities, Available-for-sale, Unrealized Loss Position	$ 8	$ 7
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	100	7
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	0	0
Debt Securities, Available-for-sale, Unrealized Loss Position, Fair Value	$ 108	$ 14
State, municipalities and political subdivisions
Available-for-sale Securities Including Securities Pledged [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Number of Positions | securities	86	21
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	$ 14	$ 1
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	$ 14	$ 1
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions | securities	86	21
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Number of Positions | securities	0	0
Debt Securities, Available-for-sale, Unrealized Loss Position	$ 0	$ 0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	167	33
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	0	0
Debt Securities, Available-for-sale, Unrealized Loss Position, Fair Value	$ 167	$ 33
U.S. corporate public securities
Available-for-sale Securities Including Securities Pledged [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Number of Positions | securities	542	290
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	$ 298	$ 39
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	$ 230	$ 32
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions | securities	729	428
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Number of Positions | securities	187	138
Debt Securities, Available-for-sale, Unrealized Loss Position	$ 362	$ 110
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	2,358	1,237
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	68	7
Debt Securities, Available-for-sale, Unrealized Loss Position, Fair Value	$ 2,720	$ 1,347
U.S. corporate private securities
Available-for-sale Securities Including Securities Pledged [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Number of Positions | securities	153	35
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	$ 77	$ 15
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	$ 62	$ 2
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions | securities	162	43
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Number of Positions | securities	9	8
Debt Securities, Available-for-sale, Unrealized Loss Position	$ 94	$ 94
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	1,352	325
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	15	13
Debt Securities, Available-for-sale, Unrealized Loss Position, Fair Value	$ 1,446	$ 419
Foreign corporate public securities and foreign governments
Available-for-sale Securities Including Securities Pledged [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Number of Positions | securities	193	90
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	$ 93	$ 14
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	$ 68	$ 13
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions | securities	235	107
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Number of Positions | securities	42	17
Debt Securities, Available-for-sale, Unrealized Loss Position	$ 152	$ 21
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	843	425
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	25	1
Debt Securities, Available-for-sale, Unrealized Loss Position, Fair Value	$ 995	$ 446
Foreign corporate private securities
Available-for-sale Securities Including Securities Pledged [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Number of Positions | securities	77	7
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	$ 28	$ 1
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	$ 28	$ 1
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions | securities	78	8
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Number of Positions | securities	1	1
Debt Securities, Available-for-sale, Unrealized Loss Position	$ 10	$ 10
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	871	54
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	0	0
Debt Securities, Available-for-sale, Unrealized Loss Position, Fair Value	$ 881	$ 64
Residential mortgage-backed
Available-for-sale Securities Including Securities Pledged [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Number of Positions | securities	300	181
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	$ 52	$ 20
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	$ 39	$ 11
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions | securities	415	277
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Number of Positions | securities	115	96
Debt Securities, Available-for-sale, Unrealized Loss Position	$ 254	$ 241
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	921	400
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	13	9
Debt Securities, Available-for-sale, Unrealized Loss Position, Fair Value	$ 1,175	$ 641
Commercial mortgage-backed
Available-for-sale Securities Including Securities Pledged [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Number of Positions | securities	376	178
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	$ 79	$ 15
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	$ 68	$ 8
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions | securities	407	205
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Number of Positions | securities	31	27
Debt Securities, Available-for-sale, Unrealized Loss Position	$ 171	$ 155
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	1,681	780
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	11	7
Debt Securities, Available-for-sale, Unrealized Loss Position, Fair Value	$ 1,852	$ 935
Other asset-backed securities
Available-for-sale Securities Including Securities Pledged [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Number of Positions | securities	294	183
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	$ 25	$ 6
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	$ 21	$ 4
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions | securities	351	231
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Number of Positions | securities	57	48
Debt Securities, Available-for-sale, Unrealized Loss Position	$ 93	$ 70
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	1,005	577
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	4	2
Debt Securities, Available-for-sale, Unrealized Loss Position, Fair Value	$ 1,098	$ 647
US Government Corporations and Agencies Securities
Available-for-sale Securities Including Securities Pledged [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Number of Positions | securities	2
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	$ 1
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	$ 1
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions | securities	2
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Number of Positions | securities	0
Debt Securities, Available-for-sale, Unrealized Loss Position	$ 0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	19
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	0
Debt Securities, Available-for-sale, Unrealized Loss Position, Fair Value	$ 19