Investments (Fair Value and Losses by Investment Category and Length of Time in a Loss Position) (Details) - USD ($) $ in Millions	Mar. 31, 2025	Dec. 31, 2024
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	$ 19,357	$ 21,494
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	600	828
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	29,911	28,394
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	5,844	5,556
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	49,268	49,888
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	6,444	6,384
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	18,594	21,046
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	577	820
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	29,470	27,877
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	5,764	5,463
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	48,064	48,923
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	6,341	6,283
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	763	448
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	23	8
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	441	517
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	80	93
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	1,204	965
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	103	101
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	14,280	14,741
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	481	529
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	19,066	18,851
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	3,610	3,682
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	33,346	33,592
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	4,091	4,211
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	758	347
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	22	7
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	280	347
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	36	50
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	1,038	694
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	58	57
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	185	286
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	3	5
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	438	469
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	45	46
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	623	755
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	48	51
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	219	354
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	3	7
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	600	593
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	84	100
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	819	947
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	87	107
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	1,580	940
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	19	19
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	1,446	1,730
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	149	159
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	3,026	2,670
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	168	178
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	5	101
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	1	1
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	31	40
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	6	5
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	36	141
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	7	6
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	360	333
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	7	4
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	937	980
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	78	91
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	1,297	1,313
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	85	95
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	202	792
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	4	15
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	673	656
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	244	266
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	875	1,448
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	248	281
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	112	155
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	3	7
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	434	417
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	83	92
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	546	572
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	86	99
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	1,308	1,408
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	49	42
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	1,757	1,816
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	348	344
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	3,065	3,224
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	397	386
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	130	130
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	38	38
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	130	130
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	38	38
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	348	2,037
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	8	192
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	4,119	2,365
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	1,123	683
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	4,467	4,402
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	$ 1,131	$ 875