Unearned revenue liability (URL Rollforward) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023	Dec. 31, 2022
Insurance [Abstract]
Balance – beginning of period	$ 680	$ 585	$ 673	$ 567
Deferred revenue	34	32
Amortization	(18)	(14)
Other (including foreign exchange)	(9)	0
Balance – end of period	$ 680	$ 585	$ 673	$ 567