Fair Value Measurements - Changes in balances of Level 3 financial assets carried at fair value (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	$ 2,290	$ 3,841	$ 3,521	$ 2,290
Total realized/unrealized gains (losses) included in Net earnings		(42)	(10)	(21)
Total realized/unrealized gains (losses) included in other comprehensive income (loss)		69	75	(39)
Purchases and issuances		781	1,578	1,828
Sales and settlements		(606)	(565)	(482)
Transfer into Level 3		620	244	270
Transfer out of Level 3		(957)	(1,002)	(325)
Financial assets, Ending Balance		3,706	3,841	3,521
Fixed maturities
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	2,102	3,387	3,164	2,102
Total realized/unrealized gains (losses) included in Net earnings		(23)	0	(22)
Total realized/unrealized gains (losses) included in other comprehensive income (loss)		69	75	(39)
Purchases and issuances		706	1,525	1,667
Sales and settlements		(587)	(563)	(476)
Transfer into Level 3		595	188	240
Transfer out of Level 3		(931)	(1,002)	(308)
Financial assets, Ending Balance		3,216	3,387	3,164
U.S. government agency
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	8	15	9	8
Total realized/unrealized gains (losses) included in Net earnings		4	0	0
Total realized/unrealized gains (losses) included in other comprehensive income (loss)		(4)	7	0
Purchases and issuances		0	0	0
Sales and settlements		0	(1)	0
Transfer into Level 3		0	0	1
Transfer out of Level 3		0	0	0
Financial assets, Ending Balance		15	15	9
State and municipal
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	148	105	59	148
Total realized/unrealized gains (losses) included in Net earnings		0	0	0
Total realized/unrealized gains (losses) included in other comprehensive income (loss)		5	5	(2)
Purchases and issuances		0	0	0
Sales and settlements		(5)	(3)	(3)
Transfer into Level 3		0	55	0
Transfer out of Level 3		(2)	(11)	(84)
Financial assets, Ending Balance		103	105	59
Residential MBS
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	122	173	197	122
Total realized/unrealized gains (losses) included in Net earnings		(7)	6	(9)
Total realized/unrealized gains (losses) included in other comprehensive income (loss)		(8)	(3)	(4)
Purchases and issuances		0	0	0
Sales and settlements		(19)	(20)	(21)
Transfer into Level 3		58	48	130
Transfer out of Level 3		(32)	(55)	(21)
Financial assets, Ending Balance		165	173	197
Commercial MBS
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	36	35	56	36
Total realized/unrealized gains (losses) included in Net earnings		0	2	0
Total realized/unrealized gains (losses) included in other comprehensive income (loss)		1	0	0
Purchases and issuances		0	0	20
Sales and settlements		(3)	(12)	0
Transfer into Level 3		2	4	0
Transfer out of Level 3		(22)	(15)	0
Financial assets, Ending Balance		13	35	56
Collateralized loan obligations
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	200	15	116	200
Total realized/unrealized gains (losses) included in Net earnings		(5)	(5)	(3)
Total realized/unrealized gains (losses) included in other comprehensive income (loss)		22	5	(13)
Purchases and issuances		0	0	35
Sales and settlements		0	0	(20)
Transfer into Level 3		187	28	3
Transfer out of Level 3		(155)	(129)	(86)
Financial assets, Ending Balance		64	15	116
Other asset-backed securities
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	544	1,286	731	544
Total realized/unrealized gains (losses) included in Net earnings		(17)	0	0
Total realized/unrealized gains (losses) included in other comprehensive income (loss)		20	6	(2)
Purchases and issuances		423	787	391
Sales and settlements		(375)	(192)	(228)
Transfer into Level 3		215	23	79
Transfer out of Level 3		(179)	(69)	(53)
Financial assets, Ending Balance		1,373	1,286	731
Corporate and other
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	1,044	1,758	1,996	1,044
Total realized/unrealized gains (losses) included in Net earnings		2	(3)	(10)
Total realized/unrealized gains (losses) included in other comprehensive income (loss)		33	55	(18)
Purchases and issuances		283	738	1,221
Sales and settlements		(185)	(335)	(204)
Transfer into Level 3		133	30	27
Transfer out of Level 3		(541)	(723)	(64)
Financial assets, Ending Balance		1,483	1,758	1,996
Equity securities
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	165	437	336	165
Total realized/unrealized gains (losses) included in Net earnings		(13)	(5)	9
Total realized/unrealized gains (losses) included in other comprehensive income (loss)		0	0	0
Purchases and issuances		73	52	155
Sales and settlements		(19)	(2)	(6)
Transfer into Level 3	29	17	56	30
Transfer out of Level 3		(26)	0	(17)
Financial assets, Ending Balance		469	437	336
Assets of MIE
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	$ 23	17	21	23
Total realized/unrealized gains (losses) included in Net earnings		(6)	(5)	(8)
Total realized/unrealized gains (losses) included in other comprehensive income (loss)		0	0	0
Purchases and issuances		2	1	6
Sales and settlements		0	0	0
Transfer into Level 3		8	0	0
Transfer out of Level 3		0	0	0
Financial assets, Ending Balance		$ 21	$ 17	$ 21