Fair Value - Rollforward of Level 3 assets and liabilities (Details) - Recurring - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Other liabilities
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period		$ (19)	$ (17)	$ (14)	$ (17)
Total gains or (losses) (realized/unrealized) - included in earnings	[1]	0	0	0	0
Total gains or (losses) (realized/unrealized) - included in other comprehensive income		0	1	0	1
Purchases, issuances, sales and settlements
Purchases		0	0	0	0
Issuances		(4)	0	(9)	0
Sales		0	0	0	0
Settlements		2	2	2	2
Transfers in and/or out of Level 3		0	0	0	0
Balance at end of period		(21)	(14)	(21)	(14)
Available for sale | Structured securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	[2]	0	3	0	3
Total gains or (losses) (realized/unrealized) - included in earnings	[1],[2]	0	(1)	0	(1)
Total gains or (losses) (realized/unrealized) - included in other comprehensive income	[2]	0	0	0	0
Purchases, issuances, sales and settlements
Purchases	[2]	0	0	0	0
Issuances	[2]	0	0	0	0
Sales	[2]	0	(2)	0	(2)
Settlements	[2]	0	0	0	0
Transfers in and/or out of Level 3	[2]	0	0	0	0
Balance at end of period	[2]	0	0	0	0
Available for sale | Corporate bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period		100	4	121	0
Total gains or (losses) (realized/unrealized) - included in earnings	[1]	0	0	1	0
Total gains or (losses) (realized/unrealized) - included in other comprehensive income		(1)	0	(1)	0
Purchases, issuances, sales and settlements
Purchases		25	0	68	0
Issuances		0	0	0	0
Sales		0	(4)	0	(4)
Settlements		0	0	(65)	0
Transfers in and/or out of Level 3		0	0	0	4
Balance at end of period		124	0	124	0
Fair value option | Other investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period		86	34	33	28
Total gains or (losses) (realized/unrealized) - included in earnings	[1]	0	0	(1)	0
Total gains or (losses) (realized/unrealized) - included in other comprehensive income		0	0	0	0
Purchases, issuances, sales and settlements
Purchases		29	1	87	12
Issuances		0	0	0	0
Sales		(6)	(1)	(10)	(3)
Settlements		(9)	0	(9)	(3)
Transfers in and/or out of Level 3		0	0	0	0
Balance at end of period		100	34	100	34
Fair value option | Short-term investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period		0	0	0	0
Total gains or (losses) (realized/unrealized) - included in earnings	[1]	0	0	0	0
Total gains or (losses) (realized/unrealized) - included in other comprehensive income		0	0	0	0
Purchases, issuances, sales and settlements
Purchases		4	0	4	0
Issuances		0	0	0	0
Sales		0	0	0	0
Settlements		0	0	0	0
Transfers in and/or out of Level 3		0	0	0	0
Balance at end of period		4	0	4	0
Fair value option | Equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period		4	5	4	5
Total gains or (losses) (realized/unrealized) - included in earnings	[1]	0	0	0	0
Total gains or (losses) (realized/unrealized) - included in other comprehensive income		0	0	0	0
Purchases, issuances, sales and settlements
Purchases		0	0	0	0
Issuances		0	0	0	0
Sales		0	0	0	0
Settlements		0	0	0	0
Transfers in and/or out of Level 3		0	0	0	0
Balance at end of period		4	5	4	5
Equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period		5	3	4	3
Total gains or (losses) (realized/unrealized) - included in earnings	[1]	0	0	0	0
Total gains or (losses) (realized/unrealized) - included in other comprehensive income		0	0	0	0
Purchases, issuances, sales and settlements
Purchases		0	0	1	0
Issuances		0	0	0	0
Sales		0	0	0	0
Settlements		0	0	0	0
Transfers in and/or out of Level 3		0	0	0	0
Balance at end of period		$ 5	$ 3	$ 5	$ 3

[1] Gains or losses were included in net realized gains (losses).

[2] Includes asset backed securities, residential mortgage backed securities and commercial mortgage backed securities.