Fair Value Measurements - Changes in balances of Level 3 financial assets carried at fair value (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	$ 3,513	$ 3,685	$ 3,841	$ 3,521
Total realized/unrealized gains (losses) included in Net income	(2)	4	(45)	8
Total realized/unrealized gains (losses) included in other comprehensive income (loss)	72	25	24	64
Purchases and issuances	263	265	465	773
Sales and settlements	(50)	(187)	(273)	(398)
Transfer into Level 3	156	41	351	57
Transfer out of Level 3	(112)	(727)	(523)	(919)
Financial assets, Ending Balance	3,840	3,106	3,840	3,106
Fixed maturities
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	3,061	3,311	3,387	3,164
Total realized/unrealized gains (losses) included in Net income	0	6	(18)	10
Total realized/unrealized gains (losses) included in other comprehensive income (loss)	72	25	24	64
Purchases and issuances	246	246	442	753
Sales and settlements	(50)	(186)	(273)	(397)
Transfer into Level 3	154	35	332	35
Transfer out of Level 3	(112)	(727)	(523)	(919)
Financial assets, Ending Balance	3,371	2,710	3,371	2,710
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	2	0
Total realized/unrealized gains (losses) included in other comprehensive income (loss)	(1)	0	(2)	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	105	63	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)	5	2	6	7
Purchases and issuances	0	0	0	0
Sales and settlements	(1)	(1)	(2)	(2)
Transfer into Level 3	0	18	0	18
Transfer out of Level 3	(2)	0	(2)	0
Financial assets, Ending Balance	107	82	107	82
Residential MBS
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	163	169	173	197
Total realized/unrealized gains (losses) included in Net income	0	4	5	9
Total realized/unrealized gains (losses) included in other comprehensive income (loss)	4	0	(8)	(5)
Purchases and issuances	0	0	0	0
Sales and settlements	(4)	(4)	(9)	(10)
Transfer into Level 3	0	2	2	2
Transfer out of Level 3	(7)	(32)	(7)	(54)
Financial assets, Ending Balance	156	139	156	139
Commercial MBS
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	32	55	35	56
Total realized/unrealized gains (losses) included in Net income	1	2	1	2
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	(2)	(3)	(3)
Transfer into Level 3	0	0	0	0
Transfer out of Level 3	0	(5)	0	(5)
Financial assets, Ending Balance	33	50	33	50
Collateralized loan obligations
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	168	37	15	116
Total realized/unrealized gains (losses) included in Net income	(3)	0	(10)	(3)
Total realized/unrealized gains (losses) included in other comprehensive income (loss)	13	0	15	6
Purchases and issuances	0	0	0	0
Sales and settlements	0	0	0	0
Transfer into Level 3	29	13	187	13
Transfer out of Level 3	0	0	0	(82)
Financial assets, Ending Balance	207	50	207	50
Other asset-backed securities
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	1,030	633	1,286	731
Total realized/unrealized gains (losses) included in Net income	0	0	(14)	0
Total realized/unrealized gains (losses) included in other comprehensive income (loss)	4	3	(7)	5
Purchases and issuances	198	17	275	92
Sales and settlements	(25)	(18)	(203)	(132)
Transfer into Level 3	121	0	134	0
Transfer out of Level 3	0	(268)	(143)	(329)
Financial assets, Ending Balance	1,328	367	1,328	367
Corporate and other
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	1,548	2,346	1,758	1,996
Total realized/unrealized gains (losses) included in Net income	1	0	(2)	2
Total realized/unrealized gains (losses) included in other comprehensive income (loss)	47	20	20	51
Purchases and issuances	48	229	167	661
Sales and settlements	(20)	(161)	(56)	(249)
Transfer into Level 3	4	2	9	2
Transfer out of Level 3	(103)	(422)	(371)	(449)
Financial assets, Ending Balance	1,525	2,014	1,525	2,014
Equity securities
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	436	354	437	336
Total realized/unrealized gains (losses) included in Net income	(1)	(1)	(25)	0
Total realized/unrealized gains (losses) included in other comprehensive income (loss)	0	0	0	0
Purchases and issuances	17	19	23	20
Sales and settlements	0	(1)	0	(1)
Transfer into Level 3	0	6	17	22
Transfer out of Level 3	0	0	0	0
Financial assets, Ending Balance	452	377	452	377
Assets of MIE
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	16	20	17	21
Total realized/unrealized gains (losses) included in Net income	(1)	(1)	(2)	(2)
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	2	0	2	0
Transfer out of Level 3	0	0	0	0
Financial assets, Ending Balance	$ 17	$ 19	$ 17	$ 19