Investments (Fair Value and Losses by Investment Category and Length of Time in a Loss Position) (Details) - USD ($) $ in Millions	Jun. 30, 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	$ 14,406	$ 4,857
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	458	183
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	33,741	36,678
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	6,049	5,370
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	48,147	41,535
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	6,507	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	14,045	4,562
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	449	147
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	33,027	35,764
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	5,919	5,186
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	47,072	40,326
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	6,368	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	361	295
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	9	36
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	714	914
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	130	184
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	1,075	1,209
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	139	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	8,885	2,134
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	217	70
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	22,555	24,207
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	4,043	3,524
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	31,440	26,341
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	4,260	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	352	295
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	8	36
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	476	649
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	68	121
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	828	944
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	76	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	404	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	15	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	449	459
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	56	33
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	853	459
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	71	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	137	115
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	1	3
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	721	681
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	108	99
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	858	796
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	109	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	794	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	2,310	3,025
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	175	223
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	3,104	3,361
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	183	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	9	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	44	68
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	5	10
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	53	68
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	6	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	270	160
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	2	5
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	1,225	1,328
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	129	190
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	1,495	1,488
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	131	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	0	4
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	1
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	0	4
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	0	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	422	614
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	4	10
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	736	717
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	252	204
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	1,158	1,331
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	256	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	114	73
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	4	1
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	785	864
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	146	128
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	899	937
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	150	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	726	254
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	11	3
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	2,110	2,290
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	362	333
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	2,836	2,544
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	373	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	194	193
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	57	52
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	194	193
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	57	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	2,293	876
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	187	50
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	2,136	2,193
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	648	452
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	4,429	3,069
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	$ 835	$ 502