Outstanding Exposure Outstanding Exposure - Schedule of Non-Financial Guaranty Exposure (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Excess Of Loss Reinsurance [Member]
Schedule of Insured Financial Obligations [Line Items]
Gross Debt Service Outstanding	$ 809	$ 773
Net Debt Service Outstanding	705	675
Aircraft Residual Value Insurance [Member]
Schedule of Insured Financial Obligations [Line Items]
Gross Debt Service Outstanding	201	201
Net Debt Service Outstanding	$ 140	$ 140