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, 2019	Dec. 31, 2018	Dec. 31, 2017
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	$ 2,290	$ 3,521	$ 2,290	$ 1,762
Total realized/unrealized gains (losses) included in Net earnings		(10)	(21)	(39)
Total realized/unrealized gains (losses) included in other comprehensive income (loss)		75	(39)	17
Purchases and issuances		1,578	1,828	1,079
Sales and settlements		(565)	(482)	(437)
Transfer into Level 3		244	270	289
Transfer out of Level 3		(1,002)	(325)	(381)
Financial assets, Ending Balance		3,841	3,521	2,290
Fixed maturities
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	2,102	3,164	2,102	1,559
Total realized/unrealized gains (losses) included in Net earnings		0	(22)	(7)
Total realized/unrealized gains (losses) included in other comprehensive income (loss)		75	(39)	7
Purchases and issuances		1,525	1,667	1,032
Sales and settlements		(563)	(476)	(421)
Transfer into Level 3		188	240	289
Transfer out of Level 3		(1,002)	(308)	(357)
Financial assets, Ending Balance		3,387	3,164	2,102
U.S. government agency
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	8	9	8	8
Total realized/unrealized gains (losses) included in Net earnings		0	0	0
Total realized/unrealized gains (losses) included in other comprehensive income (loss)		7	0	0
Purchases and issuances		0	0	0
Sales and settlements		(1)	0	0
Transfer into Level 3		0	1	0
Transfer out of Level 3		0	0	0
Financial assets, Ending Balance		15	9	8
State and municipal
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	148	59	148	140
Total realized/unrealized gains (losses) included in Net earnings		0	0	0
Total realized/unrealized gains (losses) included in other comprehensive income (loss)		5	(2)	2
Purchases and issuances		0	0	0
Sales and settlements		(3)	(3)	(2)
Transfer into Level 3		55	0	10
Transfer out of Level 3		(11)	(84)	(2)
Financial assets, Ending Balance		105	59	148
Residential MBS
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	122	197	122	190
Total realized/unrealized gains (losses) included in Net earnings		6	(9)	(4)
Total realized/unrealized gains (losses) included in other comprehensive income (loss)		(3)	(4)	2
Purchases and issuances		0	0	1
Sales and settlements		(20)	(21)	(40)
Transfer into Level 3		48	130	44
Transfer out of Level 3		(55)	(21)	(71)
Financial assets, Ending Balance		173	197	122
Commercial MBS
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	36	56	36	25
Total realized/unrealized gains (losses) included in Net earnings		2	0	2
Total realized/unrealized gains (losses) included in other comprehensive income (loss)		0	0	0
Purchases and issuances		0	20	15
Sales and settlements		(12)	0	(10)
Transfer into Level 3		4	0	4
Transfer out of Level 3		(15)	0	0
Financial assets, Ending Balance		35	56	36
Collateralized loan obligations
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	200	116	200	174
Total realized/unrealized gains (losses) included in Net earnings		(5)	(3)	(1)
Total realized/unrealized gains (losses) included in other comprehensive income (loss)		5	(13)	(1)
Purchases and issuances		0	35	55
Sales and settlements		0	(20)	(27)
Transfer into Level 3		28	3	0
Transfer out of Level 3		(129)	(86)	0
Financial assets, Ending Balance		15	116	200
Other asset-backed securities
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	544	731	544	310
Total realized/unrealized gains (losses) included in Net earnings		0	0	1
Total realized/unrealized gains (losses) included in other comprehensive income (loss)		6	(2)	2
Purchases and issuances		787	391	355
Sales and settlements		(192)	(228)	(105)
Transfer into Level 3		23	79	202
Transfer out of Level 3		(69)	(53)	(221)
Financial assets, Ending Balance		1,286	731	544
Corporate and other
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	1,044	1,996	1,044	712
Total realized/unrealized gains (losses) included in Net earnings		(3)	(10)	(5)
Total realized/unrealized gains (losses) included in other comprehensive income (loss)		55	(18)	2
Purchases and issuances		738	1,221	606
Sales and settlements		(335)	(204)	(237)
Transfer into Level 3		30	27	29
Transfer out of Level 3		(723)	(64)	(63)
Financial assets, Ending Balance		1,758	1,996	1,044
Equity securities
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	165	336	165	174
Total realized/unrealized gains (losses) included in Net earnings		(5)	9	(21)
Total realized/unrealized gains (losses) included in other comprehensive income (loss)		0	0	10
Purchases and issuances		52	155	38
Sales and settlements		(2)	(6)	(16)
Transfer into Level 3	29	56	30	0
Transfer out of Level 3		0	(17)	(20)
Financial assets, Ending Balance		437	336	165
Assets of MIE
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	$ 23	21	23	29
Total realized/unrealized gains (losses) included in Net earnings		(5)	(8)	(11)
Total realized/unrealized gains (losses) included in other comprehensive income (loss)		0	0	0
Purchases and issuances		1	6	9
Sales and settlements		0	0	0
Transfer into Level 3		0	0	0
Transfer out of Level 3		0	0	(4)
Financial assets, Ending Balance		$ 17	$ 21	$ 23