Transactions With Affliated Parties (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Related Party Transaction
Payment for commissions	$ 7	$ 7	$ 7
Earned premiums	4,954	4,710	4,480
Affiliated Parties
Related Party Transaction
Earned premiums	$ 45	$ 44	$ 42