Fair value measurements (Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation) (Details) - Level 3 - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance- Beginning of year, assets	$ 77	$ 73	$ 69
Transfers into Level 3, assets	1	0	0
Transfers out of Level 3, assets	0	0	(3)
Change in Net Unrealized Gains (Losses) included in OCI, Assets	0	0	0
Net Realized Gains/Losses, Assets	15	8	1
Purchased, assets	9	21	23
Sales, assets	(12)	(25)	(17)
Settlements, assets	0	0	0
Other, assets	0	0	0
Balance- End of year, assets	90	77	73
Net Realized Gains/Losses Attributable to Changes in Fair Value at the Balance Sheet Date, Assets	14	5	4
Change in Net Unrealized Gains/Losses included in OCI at the Balance Sheet Date, Assets	0	0	0
Short-term investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance- Beginning of year, assets	7	5	6
Transfers into Level 3, assets	0	0	0
Transfers out of Level 3, assets	0	0	0
Change in Net Unrealized Gains (Losses) included in OCI, Assets	0	(1)	0
Net Realized Gains/Losses, Assets	(2)	0	(1)
Purchased, assets	3	9	14
Sales, assets	0	0	(2)
Settlements, assets	(5)	(6)	(12)
Other, assets	0	0	0
Balance- End of year, assets	3	7	5
Net Realized Gains/Losses Attributable to Changes in Fair Value at the Balance Sheet Date, Assets	(1)	0	0
Change in Net Unrealized Gains/Losses included in OCI at the Balance Sheet Date, Assets	0	0	0
Other investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance- Beginning of year, assets	0	10	10
Transfers into Level 3, assets		0	0
Transfers out of Level 3, assets		(10)	0
Change in Net Unrealized Gains (Losses) included in OCI, Assets		0	0
Net Realized Gains/Losses, Assets		0	0
Purchased, assets		0	0
Sales, assets		0	0
Settlements, assets		0	0
Other, assets		0	0
Balance- End of year, assets		0	10
Net Realized Gains/Losses Attributable to Changes in Fair Value at the Balance Sheet Date, Assets		0	0
Change in Net Unrealized Gains/Losses included in OCI at the Balance Sheet Date, Assets		0	0
Available-for-sale Securities [Member] | Non-U.S.
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance- Beginning of year, assets	633	546	449
Transfers into Level 3, assets	23	24	0
Transfers out of Level 3, assets	(23)	(11)	(16)
Change in Net Unrealized Gains (Losses) included in OCI, Assets	(53)	(30)	19
Net Realized Gains/Losses, Assets	(6)	(1)	(1)
Purchased, assets	156	275	274
Sales, assets	(59)	(48)	(122)
Settlements, assets	(107)	(122)	(57)
Other, assets	0	0	0
Balance- End of year, assets	564	633	546
Net Realized Gains/Losses Attributable to Changes in Fair Value at the Balance Sheet Date, Assets	(2)	0	0
Change in Net Unrealized Gains/Losses included in OCI at the Balance Sheet Date, Assets	(53)	(25)	16
Available-for-sale Securities [Member] | Corporate and asset-backed securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance- Beginning of year, assets	2,049	1,573	1,451
Transfers into Level 3, assets	47	91	134
Transfers out of Level 3, assets	(97)	(76)	(73)
Change in Net Unrealized Gains (Losses) included in OCI, Assets	(80)	15	(8)
Net Realized Gains/Losses, Assets	(14)	(2)	(30)
Purchased, assets	921	1,154	708
Sales, assets	(85)	(99)	(186)
Settlements, assets	(292)	(607)	(423)
Other, assets	0	0	0
Balance- End of year, assets	2,449	2,049	1,573
Net Realized Gains/Losses Attributable to Changes in Fair Value at the Balance Sheet Date, Assets	(9)	3	(5)
Change in Net Unrealized Gains/Losses included in OCI at the Balance Sheet Date, Assets	(84)	17	(6)
Available-for-sale Securities [Member] | Mortgage-backed securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance- Beginning of year, assets	26	60	60
Transfers into Level 3, assets	0	0	0
Transfers out of Level 3, assets	(9)	(18)	(1)
Change in Net Unrealized Gains (Losses) included in OCI, Assets	0	0	0
Net Realized Gains/Losses, Assets	0	0	0
Purchased, assets	4	18	2
Sales, assets	0	(1)	0
Settlements, assets	(10)	(33)	(1)
Other, assets	0	0	0
Balance- End of year, assets	11	26	60
Net Realized Gains/Losses Attributable to Changes in Fair Value at the Balance Sheet Date, Assets	0	0	0
Change in Net Unrealized Gains/Losses included in OCI at the Balance Sheet Date, Assets	$ 0	$ 0	$ 0