Fair Value Measurements - Changes in balances of Level 3 financial assets carried at fair value (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	$ 3,840	$ 3,106	$ 3,841	$ 3,521
Total realized/unrealized gains (losses) included in Net income	(13)	(8)	(58)	0
Total realized/unrealized gains (losses) included in other comprehensive income (loss)	23	23	47	87
Purchases and issuances	104	399	569	1,172
Sales and settlements	(159)	(90)	(432)	(488)
Transfer into Level 3	247	88	598	145
Transfer out of Level 3	(237)	(2)	(760)	(921)
Financial assets, Ending Balance	3,805	3,516	3,805	3,516
Fixed maturities
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	3,371	2,710	3,387	3,164
Total realized/unrealized gains (losses) included in Net income	(1)	0	(19)	10
Total realized/unrealized gains (losses) included in other comprehensive income (loss)	23	23	47	87
Purchases and issuances	92	381	534	1,134
Sales and settlements	(159)	(88)	(432)	(485)
Transfer into Level 3	247	54	579	89
Transfer out of Level 3	(227)	(2)	(750)	(921)
Financial assets, Ending Balance	3,346	3,078	3,346	3,078
U.S. government agency
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	15	8	15	9
Total realized/unrealized gains (losses) included in Net income	1	0	3	0
Total realized/unrealized gains (losses) included in other comprehensive income (loss)	(1)	0	(3)	0
Purchases and issuances	0	0	0	0
Sales and settlements	0	0	0	(1)
Transfer into Level 3	0	0	0	0
Transfer out of Level 3	0	0	0	0
Financial assets, Ending Balance	15	8	15	8
State and municipal
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	107	82	105	59
Total realized/unrealized gains (losses) included in Net income	0	0	0	0
Total realized/unrealized gains (losses) included in other comprehensive income (loss)	0	2	6	9
Purchases and issuances	0	0	0	0
Sales and settlements	(1)	0	(3)	(2)
Transfer into Level 3	0	18	0	36
Transfer out of Level 3	0	0	(2)	0
Financial assets, Ending Balance	106	102	106	102
Residential MBS
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	156	139	173	197
Total realized/unrealized gains (losses) included in Net income	(4)	1	1	10
Total realized/unrealized gains (losses) included in other comprehensive income (loss)	1	(1)	(7)	(6)
Purchases and issuances	0	0	0	0
Sales and settlements	(6)	(4)	(15)	(14)
Transfer into Level 3	49	22	51	24
Transfer out of Level 3	(18)	(1)	(25)	(55)
Financial assets, Ending Balance	178	156	178	156
Commercial MBS
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	33	50	35	56
Total realized/unrealized gains (losses) included in Net income	(1)	1	0	3
Total realized/unrealized gains (losses) included in other comprehensive income (loss)	0	0	0	0
Purchases and issuances	0	0	0	0
Sales and settlements	0	0	(3)	(3)
Transfer into Level 3	0	4	0	4
Transfer out of Level 3	(22)	0	(22)	(5)
Financial assets, Ending Balance	10	55	10	55
Collateralized loan obligations
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	207	50	15	116
Total realized/unrealized gains (losses) included in Net income	(1)	(2)	(11)	(5)
Total realized/unrealized gains (losses) included in other comprehensive income (loss)	6	1	21	7
Purchases and issuances	0	8	0	8
Sales and settlements	0	0	0	0
Transfer into Level 3	0	0	187	13
Transfer out of Level 3	0	0	0	(82)
Financial assets, Ending Balance	212	57	212	57
Other asset-backed securities
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	1,328	367	1,286	731
Total realized/unrealized gains (losses) included in Net income	(2)	0	(16)	0
Total realized/unrealized gains (losses) included in other comprehensive income (loss)	13	1	6	6
Purchases and issuances	39	49	314	141
Sales and settlements	(75)	(3)	(278)	(135)
Transfer into Level 3	77	0	211	0
Transfer out of Level 3	(36)	0	(179)	(329)
Financial assets, Ending Balance	1,344	414	1,344	414
Corporate and other
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	1,525	2,014	1,758	1,996
Total realized/unrealized gains (losses) included in Net income	6	0	4	2
Total realized/unrealized gains (losses) included in other comprehensive income (loss)	4	20	24	71
Purchases and issuances	53	324	220	985
Sales and settlements	(77)	(81)	(133)	(330)
Transfer into Level 3	121	10	130	12
Transfer out of Level 3	(151)	(1)	(522)	(450)
Financial assets, Ending Balance	1,481	2,286	1,481	2,286
Equity securities
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	452	377	437	336
Total realized/unrealized gains (losses) included in Net income	(10)	(7)	(35)	(7)
Total realized/unrealized gains (losses) included in other comprehensive income (loss)	0	0	0	0
Purchases and issuances	12	18	35	38
Sales and settlements	0	(2)	0	(3)
Transfer into Level 3	0	34	17	56
Transfer out of Level 3	(10)	0	(10)	0
Financial assets, Ending Balance	444	420	444	420
Assets of MIE
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	17	19	17	21
Total realized/unrealized gains (losses) included in Net income	(2)	(1)	(4)	(3)
Total realized/unrealized gains (losses) included in other comprehensive income (loss)	0	0	0	0
Purchases and issuances	0	0	0	0
Sales and settlements	0	0	0	0
Transfer into Level 3	0	0	2	0
Transfer out of Level 3	0	0	0	0
Financial assets, Ending Balance	$ 15	$ 18	$ 15	$ 18