Investments (Fair Value and Losses by Investment Category and Length of Time in a Loss Position) (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Estimated Fair Values And Gross Unrealized Losses, OTTI Impairment Losses Reported In AOCI [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	$ 10,684	$ 4,857
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	227	183
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	35,418	36,678
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	5,548	5,370
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	46,102	41,535
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	5,775	5,553
Investment grade securities
Estimated Fair Values And Gross Unrealized Losses, OTTI Impairment Losses Reported In AOCI [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	10,428	4,562
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	201	147
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	34,647	35,764
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	5,421	5,186
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	45,075	40,326
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	5,622	5,333
Non-investment grade securities
Estimated Fair Values And Gross Unrealized Losses, OTTI Impairment Losses Reported In AOCI [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	256	295
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	26	36
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	771	914
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	127	184
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	1,027	1,209
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	153	220
Corporate Debt Securities [Member] | Investment grade securities
Estimated Fair Values And Gross Unrealized Losses, OTTI Impairment Losses Reported In AOCI [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	4,063	2,134
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	89	70
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	23,710	24,207
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	3,753	3,524
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	27,773	26,341
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	3,842	3,594
Corporate Debt Securities [Member] | Non-investment grade securities
Estimated Fair Values And Gross Unrealized Losses, OTTI Impairment Losses Reported In AOCI [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	246	295
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	25	36
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	512	649
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	66	121
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	758	944
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	91	157
Canadian and Canadian provincial governments | Investment grade securities
Estimated Fair Values And Gross Unrealized Losses, OTTI Impairment Losses Reported In AOCI [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	291	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	14	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	433	459
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	54	33
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	724	459
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	68	33
Residential mortgage-backed securities | Investment grade securities
Estimated Fair Values And Gross Unrealized Losses, OTTI Impairment Losses Reported In AOCI [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	161	115
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	3	3
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	683	681
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	107	99
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	844	796
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	110	102
Asset-backed Securities [Member] | Investment grade securities
Estimated Fair Values And Gross Unrealized Losses, OTTI Impairment Losses Reported In AOCI [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	560	336
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	8	5
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	2,883	3,025
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	191	223
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	3,443	3,361
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	199	228
Asset-backed Securities [Member] | Non-investment grade securities
Estimated Fair Values And Gross Unrealized Losses, OTTI Impairment Losses Reported In AOCI [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	10	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	1	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	62	68
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	7	10
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	72	68
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	8	10
Commercial mortgage-backed securities | Investment grade securities
Estimated Fair Values And Gross Unrealized Losses, OTTI Impairment Losses Reported In AOCI [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	108	160
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	1	5
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	1,266	1,328
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	143	190
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	1,374	1,488
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	144	195
Commercial mortgage-backed securities | Non-investment grade securities
Estimated Fair Values And Gross Unrealized Losses, OTTI Impairment Losses Reported In AOCI [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	0	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	4	4
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	1	1
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	4	4
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	1	1
US Government Agencies Debt Securities [Member] | Investment grade securities
Estimated Fair Values And Gross Unrealized Losses, OTTI Impairment Losses Reported In AOCI [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	1,932	614
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	14	10
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	654	717
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	230	204
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	2,586	1,331
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	244	214
US States and Political Subdivisions Debt Securities [Member] | Investment grade securities
Estimated Fair Values And Gross Unrealized Losses, OTTI Impairment Losses Reported In AOCI [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	119	73
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	3	1
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	815	864
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	136	128
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	934	937
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	139	129
Debt Security, Government, Non-US [Member] | Investment grade securities
Estimated Fair Values And Gross Unrealized Losses, OTTI Impairment Losses Reported In AOCI [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	466	254
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	6	3
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	2,190	2,290
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	348	333
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	2,656	2,544
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	354	336
Debt Security, Government, Non-US [Member] | Non-investment grade securities
Estimated Fair Values And Gross Unrealized Losses, OTTI Impairment Losses Reported In AOCI [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	0	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	193	193
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	53	52
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	193	193
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	53	52
JAPAN | Investment grade securities
Estimated Fair Values And Gross Unrealized Losses, OTTI Impairment Losses Reported In AOCI [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	2,728	876
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	63	50
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	2,013	2,193
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	459	452
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	4,741	3,069
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	$ 522	$ 502