Future policy benefits (Rollforward) (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023	Dec. 31, 2022
Liability for Future Policy Benefit, Activity [Line Items]
Deferred profit liability		$ 1,351	$ 952
Net liability for future policy benefits, before reinsurance recoverable		14,375	10,782	$ 13,888
Less: Reinsurance recoverable on future policy benefits	[1]	272		280
Segment Life [Member]
Liability for Future Policy Benefit, Activity [Line Items]
Balance – beginning of period		16,036	14,867
Beginning balance at original discount rate				16,693	$ 15,529
Effect of changes in cash flow assumptions				185	(769)
Effect of actual variances from expected experience				(16)	(104)
Adjusted beginning of period balance		16,862	14,656
Issuances		1,059	394
Interest accrual		174	171
Net premiums collected (1)	[2]	(737)	(459)
Other (including foreign exchange)		73	(95)
Ending balance at original discount rate		17,431	14,667
Effect of changes in discount rate assumptions		(684)	(319)
Balance – end of period		16,747	14,348
Balance – beginning of period		27,462	23,324
Beginning balance at original discount rate				28,303	24,456
Effect of changes in cash flow assumptions				194	(776)
Effect of actual variances from expected experience				(6)	(98)
Adjusted beginning of period balance		28,491	23,582
Issuances		1,059	394
Interest accrual		260	242
Benefits payments		(550)	(476)
Other (including foreign exchange)		163	(67)
Ending balance at original discount rate		29,423	23,675
Effect of changes in discount rate assumptions		(801)	(623)
Balance – end of period		28,622	23,052
Net liability for future policy benefits		11,875	8,704
Deferred profit liability		1,351	952
Net liability for future policy benefits, before reinsurance recoverable		13,226	9,656
Less: Reinsurance recoverable on future policy benefits		266	250
Net liability for future policy benefits, after reinsurance recoverable		$ 12,960	$ 9,406
Weighted average duration (years)		19 years 3 months 18 days	17 years 8 months 12 days
Other Segments
Liability for Future Policy Benefit, Activity [Line Items]
Net liability for future policy benefits, before reinsurance recoverable		$ 1,149	$ 1,126
Term Life Insurance | Segment Life [Member]
Liability for Future Policy Benefit, Activity [Line Items]
Balance – beginning of period		1,590	1,806
Beginning balance at original discount rate				1,992	1,867
Effect of changes in cash flow assumptions				6	17
Effect of actual variances from expected experience				(1)	(6)
Adjusted beginning of period balance		1,997	1,878
Issuances		65	36
Interest accrual		14	28
Net premiums collected (1)	[2]	(57)	(44)
Other (including foreign exchange)		(5)	35
Ending balance at original discount rate		2,014	1,933
Effect of changes in discount rate assumptions		(407)	(48)
Balance – end of period		1,607	1,885
Balance – beginning of period		2,254	2,321
Beginning balance at original discount rate				2,749	2,447
Effect of changes in cash flow assumptions				8	20
Effect of actual variances from expected experience				3	(3)
Adjusted beginning of period balance		2,760	2,464
Issuances		65	36
Interest accrual		19	32
Benefits payments		(59)	(46)
Other (including foreign exchange)		30	72
Ending balance at original discount rate		2,815	2,558
Effect of changes in discount rate assumptions		(516)	(118)
Balance – end of period		2,299	2,440
Net liability for future policy benefits		692	555
Deferred profit liability		254	223
Net liability for future policy benefits, before reinsurance recoverable		946	778
Less: Reinsurance recoverable on future policy benefits		107	105
Net liability for future policy benefits, after reinsurance recoverable		$ 839	$ 673
Weighted average duration (years)		10 years 2 months 12 days	9 years 4 months 24 days
Whole Life Insurance | Segment Life [Member]
Liability for Future Policy Benefit, Activity [Line Items]
Balance – beginning of period		$ 3,950	$ 2,308
Beginning balance at original discount rate				3,945	2,361
Effect of changes in cash flow assumptions				70	(1)
Effect of actual variances from expected experience				22	(8)
Adjusted beginning of period balance		4,037	2,352
Issuances		295	69
Interest accrual		27	18
Net premiums collected (1)	[2]	(310)	(82)
Other (including foreign exchange)		(4)	8
Ending balance at original discount rate		4,045	2,365
Effect of changes in discount rate assumptions		18	(8)
Balance – end of period		4,063	2,357
Balance – beginning of period		10,063	5,696
Beginning balance at original discount rate				9,991	5,874
Effect of changes in cash flow assumptions				86	(1)
Effect of actual variances from expected experience				27	(7)
Adjusted beginning of period balance		10,104	5,866
Issuances		295	69
Interest accrual		74	52
Benefits payments		(87)	(65)
Other (including foreign exchange)		(2)	28
Ending balance at original discount rate		10,384	5,950
Effect of changes in discount rate assumptions		184	(42)
Balance – end of period		10,568	5,908
Net liability for future policy benefits		6,505	3,551
Deferred profit liability		904	581
Net liability for future policy benefits, before reinsurance recoverable		7,409	4,132
Less: Reinsurance recoverable on future policy benefits		45	33
Net liability for future policy benefits, after reinsurance recoverable		$ 7,364	$ 4,099
Weighted average duration (years)		25 years 7 months 6 days	25 years 3 months 18 days
Accident and Health Insurance Product Line [Member] | Segment Life [Member]
Liability for Future Policy Benefit, Activity [Line Items]
Balance – beginning of period		$ 10,432	$ 10,711
Beginning balance at original discount rate				10,692	11,258
Effect of changes in cash flow assumptions				109	(786)
Effect of actual variances from expected experience				(37)	(89)
Adjusted beginning of period balance		10,764	10,383
Issuances		697	288
Interest accrual		133	125
Net premiums collected (1)	[2]	(363)	(327)
Other (including foreign exchange)		82	(139)
Ending balance at original discount rate		11,313	10,330
Effect of changes in discount rate assumptions		(295)	(263)
Balance – end of period		11,018	10,067
Balance – beginning of period		14,650	15,038
Beginning balance at original discount rate				15,071	15,855
Effect of changes in cash flow assumptions				100	(798)
Effect of actual variances from expected experience				(36)	(87)
Adjusted beginning of period balance		15,135	14,970
Issuances		697	288
Interest accrual		164	156
Benefits payments		(398)	(362)
Other (including foreign exchange)		114	(153)
Ending balance at original discount rate		15,712	14,899
Effect of changes in discount rate assumptions		(487)	(463)
Balance – end of period		15,225	14,436
Net liability for future policy benefits		4,207	4,369
Deferred profit liability		174	135
Net liability for future policy benefits, before reinsurance recoverable		4,381	4,504
Less: Reinsurance recoverable on future policy benefits		113	112
Net liability for future policy benefits, after reinsurance recoverable		$ 4,268	$ 4,392
Weighted average duration (years)		10 years 1 month 6 days	10 years 8 months 12 days
Insurance, Other | Segment Life [Member]
Liability for Future Policy Benefit, Activity [Line Items]
Balance – beginning of period		$ 64	$ 42
Beginning balance at original discount rate				64	43
Effect of changes in cash flow assumptions				0	1
Effect of actual variances from expected experience				0	(1)
Adjusted beginning of period balance		64	43
Issuances		2	1
Interest accrual		0	0
Net premiums collected (1)	[2]	(7)	(6)
Other (including foreign exchange)		0	1
Ending balance at original discount rate		59	39
Effect of changes in discount rate assumptions		0	0
Balance – end of period		59	39
Balance – beginning of period		495	269
Beginning balance at original discount rate				492	280
Effect of changes in cash flow assumptions				0	3
Effect of actual variances from expected experience				$ 0	$ (1)
Adjusted beginning of period balance		492	282
Issuances		2	1
Interest accrual		3	2
Benefits payments		(6)	(3)
Other (including foreign exchange)		21	(14)
Ending balance at original discount rate		512	268
Effect of changes in discount rate assumptions		18	0
Balance – end of period		530	268
Net liability for future policy benefits		471	229
Deferred profit liability		19	13
Net liability for future policy benefits, before reinsurance recoverable		490	242
Less: Reinsurance recoverable on future policy benefits		1	0
Net liability for future policy benefits, after reinsurance recoverable		$ 489	$ 242
Weighted average duration (years)		15 years 1 month 6 days	14 years 6 months

[1] Net of valuation allowance for uncollectible reinsurance.

[2] Net premiums collected represent the portion of gross premiums collected from policyholders that is used to fund expected benefit.