Reinsurance (Reinsurance on premiums - short-duration contracts) (Details 3) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Premiums Earned, Net, by Business [Abstract]
Total net earned premiums	$ 1,394	$ 1,491	$ 1,455
Property and casualty [Member]
Premiums Written, Net [Abstract]
Direct premiums written	1,119	1,085	1,093
Ceded premiums written	(171)	(20)	(19)
Total net written premiums	948	1,065	1,074
Premiums Earned, Net, by Business [Abstract]
Direct premiums earned	1,107	1,094	1,068
Ceded premiums earned	(123)	(20)	(19)
Total net earned premiums	$ 984	$ 1,074	$ 1,049