Premiums Receivable and Other Insurance Assets Premiums Receivable and Other Insurance Assets (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Premiums Receivable and Other Insurance Assets [Abstract]
Prepaid Reinsurance Premiums	$ 507	$ 439
Reinsurance Recoverables, Incurred but Not Reported Claims	108	108
Reinsurance Recoverables on Paid Losses, Gross	19	20
Premiums Receivable, Net	84	80
Deferred Policy Acquisition Costs	1,329	1,258
Premiums receivable and other insurance assets	$ 2,047	$ 1,905