Fair Value Measurements - Changes in balances of Level 3 financial assets carried at fair value (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	$ 3,841	$ 3,521
Total realized/unrealized gains (losses) included in Net income	(43)	4
Total realized/unrealized gains (losses) included in other comprehensive income (loss)	(48)	39
Purchases and issuances	202	508
Sales and settlements	(223)	(211)
Transfer into Level 3	195	16
Transfer out of Level 3	(411)	(192)
Financial assets, Ending Balance	3,513	3,685
Fixed maturities
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	3,387	3,164
Total realized/unrealized gains (losses) included in Net income	(18)	4
Total realized/unrealized gains (losses) included in other comprehensive income (loss)	(48)	39
Purchases and issuances	196	507
Sales and settlements	(223)	(211)
Transfer into Level 3	178	0
Transfer out of Level 3	(411)	(192)
Financial assets, Ending Balance	3,061	3,311
U.S. government agency
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	15	9
Total realized/unrealized gains (losses) included in Net income	1	0
Total realized/unrealized gains (losses) included in other comprehensive income (loss)	(1)	0
Purchases and issuances	0	0
Sales and settlements	0	(1)
Transfer into Level 3	0	0
Transfer out of Level 3	0	0
Financial assets, Ending Balance	15	8
State and municipal
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	105	59
Total realized/unrealized gains (losses) included in Net income	0	0
Total realized/unrealized gains (losses) included in other comprehensive income (loss)	1	5
Purchases and issuances	0	0
Sales and settlements	(1)	(1)
Transfer into Level 3	0	0
Transfer out of Level 3	0	0
Financial assets, Ending Balance	105	63
Residential MBS
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	173	197
Total realized/unrealized gains (losses) included in Net income	5	5
Total realized/unrealized gains (losses) included in other comprehensive income (loss)	(12)	(5)
Purchases and issuances	0	0
Sales and settlements	(5)	(6)
Transfer into Level 3	2	0
Transfer out of Level 3	0	(22)
Financial assets, Ending Balance	163	169
Commercial MBS
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	35	56
Total realized/unrealized gains (losses) included in Net income	0	0
Total realized/unrealized gains (losses) included in other comprehensive income (loss)	0	0
Purchases and issuances	0	0
Sales and settlements	(3)	(1)
Transfer into Level 3	0	0
Transfer out of Level 3	0	0
Financial assets, Ending Balance	32	55
Collateralized loan obligations
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	15	116
Total realized/unrealized gains (losses) included in Net income	(7)	0
Total realized/unrealized gains (losses) included in other comprehensive income (loss)	2	0
Purchases and issuances	0	0
Sales and settlements	0	0
Transfer into Level 3	158	0
Transfer out of Level 3	0	0
Financial assets, Ending Balance	168	116
Other asset-backed securities
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	1,286	731
Total realized/unrealized gains (losses) included in Net income	(14)	(3)
Total realized/unrealized gains (losses) included in other comprehensive income (loss)	(11)	8
Purchases and issuances	77	75
Sales and settlements	(178)	(114)
Transfer into Level 3	13	0
Transfer out of Level 3	(143)	(143)
Financial assets, Ending Balance	1,030	554
Corporate and other
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	1,758	1,996
Total realized/unrealized gains (losses) included in Net income	(3)	2
Total realized/unrealized gains (losses) included in other comprehensive income (loss)	(27)	31
Purchases and issuances	119	432
Sales and settlements	(36)	(88)
Transfer into Level 3	5	0
Transfer out of Level 3	(268)	(27)
Financial assets, Ending Balance	1,548	2,346
Equity securities
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	437	336
Total realized/unrealized gains (losses) included in Net income	(24)	1
Total realized/unrealized gains (losses) included in other comprehensive income (loss)	0	0
Purchases and issuances	6	1
Sales and settlements	0	0
Transfer into Level 3	17	16
Transfer out of Level 3	0	0
Financial assets, Ending Balance	436	354
Assets of MIE
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	17	21
Total realized/unrealized gains (losses) included in Net income	(1)	(1)
Total realized/unrealized gains (losses) included in other comprehensive income (loss)	0	0
Purchases and issuances	0	0
Sales and settlements	0	0
Transfer into Level 3	0	0
Transfer out of Level 3	0	0
Financial assets, Ending Balance	$ 16	$ 20