Reinsurance (Reinsurance on premiums - short-duration contracts) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Earned Premiums [Abstract]
Net premiums	$ 1,426	$ 1,394	$ 1,491
Property and casualty [Member]
Written Premiums [Abstract]
Direct written premiums	1,101	1,119	1,085
Ceded written premiums	(55)	(171)	(20)
Total net written premiums	1,046	948	1,065
Earned Premiums [Abstract]
Direct earned premiums	1,124	1,107	1,094
Ceded earned premiums	(94)	(123)	(20)
Net premiums	$ 1,030	$ 984	$ 1,074