Fair Value - Rollforward of Level 3 assets and liabilities (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2023	Dec. 31, 2022
Other liabilities
Level 3 liabilities rollforward
Balance at beginning of year		$ (14)	$ (17)
Total gains or (losses) (realized/unrealized) - included in earnings	[1]	(1)	0
Total gains or (losses) (realized/unrealized) - included in other comprehensive income		0	1
Purchases, issuances, sales and settlements
Purchases		0	0
Issuances		(9)	0
Sales		0	0
Settlements		2	2
Transfers in and/or out of Level 3		0	0
Balance at end of year		(22)	(14)
Equity securities
Level 3 assets rollforward
Balance at beginning of year		4	3
Total gains or (losses) (realized/unrealized) - included in earnings	[1]	0	0
Total gains or (losses) (realized/unrealized) - included in other comprehensive income		0	0
Purchases, issuances, sales and settlements
Purchases		1	1
Issuances		0	0
Sales		0	0
Settlements		0	0
Transfers in and/or out of Level 3		0	0
Balance at end of year		5	4
Available for sale | Structured securities
Level 3 assets rollforward
Balance at beginning of year	[2]	0	3
Total gains or (losses) (realized/unrealized) - included in earnings	[1],[2]	0	(1)
Total gains or (losses) (realized/unrealized) - included in other comprehensive income	[2]	0	0
Purchases, issuances, sales and settlements
Purchases	[2]	0	0
Issuances	[2]	0	0
Sales	[2]	0	(2)
Settlements	[2]	0	0
Transfers in and/or out of Level 3	[2]	0	0
Balance at end of year	[2]	0	0
Available for sale | Corporate bonds
Level 3 assets rollforward
Balance at beginning of year		121	0
Total gains or (losses) (realized/unrealized) - included in earnings	[1]	1	0
Total gains or (losses) (realized/unrealized) - included in other comprehensive income		(1)	(1)
Purchases, issuances, sales and settlements
Purchases		111	150
Issuances		0	0
Sales		0	(6)
Settlements		(85)	(26)
Transfers in and/or out of Level 3		0	4
Balance at end of year		147	121
Available for sale | Short-term investments
Level 3 assets rollforward
Balance at beginning of year		0	0
Total gains or (losses) (realized/unrealized) - included in earnings	[1]	0	0
Total gains or (losses) (realized/unrealized) - included in other comprehensive income		0	0
Purchases, issuances, sales and settlements
Purchases		84	0
Issuances		0	0
Sales		0	0
Settlements		0	0
Transfers in and/or out of Level 3		0	0
Balance at end of year		84	0
Fair value option | Other investments
Level 3 assets rollforward
Balance at beginning of year		33	28
Total gains or (losses) (realized/unrealized) - included in earnings	[1]	(5)	(1)
Total gains or (losses) (realized/unrealized) - included in other comprehensive income		0	0
Purchases, issuances, sales and settlements
Purchases		107	12
Issuances		0	0
Sales		(10)	(3)
Settlements		(19)	(3)
Transfers in and/or out of Level 3		0	0
Balance at end of year		106	33
Fair value option | Short-term investments
Level 3 assets rollforward
Balance at beginning of year		0	0
Total gains or (losses) (realized/unrealized) - included in earnings	[1]	0	0
Total gains or (losses) (realized/unrealized) - included in other comprehensive income		0	0
Purchases, issuances, sales and settlements
Purchases		11	0
Issuances		0	0
Sales		0	0
Settlements		(1)	0
Transfers in and/or out of Level 3		0	0
Balance at end of year		10	0
Fair value option | Equity securities
Level 3 assets rollforward
Balance at beginning of year		4	5
Total gains or (losses) (realized/unrealized) - included in earnings	[1]	0	(1)
Total gains or (losses) (realized/unrealized) - included in other comprehensive income		0	0
Purchases, issuances, sales and settlements
Purchases		0	0
Issuances		0	0
Sales		0	0
Settlements		0	0
Transfers in and/or out of Level 3		0	0
Balance at end of year		$ 4	$ 4

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

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