Reinsurance and indemnification - Claims expense, life contract benefits and interest credited to contractholder funds (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Property and casualty insurance claims and claims expense
Reductions to costs and expenses due to reinsurance ceded amounts
Ceded losses incurred	$ (210)	$ (158)	$ (341)	$ (249)
Life contract benefits
Reductions to costs and expenses due to reinsurance ceded amounts
Ceded losses incurred	(45)	5	(136)	(18)
Interest credited to contractholder funds
Reductions to costs and expenses due to reinsurance ceded amounts
Ceded losses incurred	$ (7)	$ (5)	$ (12)	$ (8)