Reinsurance (Reinsurance on premiums - short-duration contracts) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Earned Premiums [Abstract]
Premiums	$ 1,395	$ 2,224	$ 2,467
Property and casualty [Member]
Written Premiums [Abstract]
Direct written premiums		864	1,101
Ceded written premiums		(23)	(55)
Total net written premiums		841	1,046
Earned Premiums [Abstract]
Direct earned premiums		841	1,124
Ceded earned premiums		(24)	(94)
Premiums		$ 817	$ 1,030