Premiums Receivable and Other Insurance Assets Premiums Receivable and Other Insurance Assets (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Premiums Receivable and Other Insurance Assets [Abstract]
Prepaid reinsurance premiums	$ 527	$ 507
Reinsurance recoverables on unpaid losses	96	108
Reinsurance recoverable on paid losses	22	19
Premiums receivable	88	84
Deferred policy acquisition costs	1,593	1,329
Total premiums receivable and other insurance assets	$ 2,326	$ 2,047