Summarized Financial Information of Unconsolidated Affiliate Summarized Balance Sheet of Unconsolidated Affiliates (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Financial Support for Nonconsolidated Legal Entity [Line Items]
Non-current Assets of Unconsolidated Affiliates	$ 18	$ 18
Current Assets of Unconsolidated Affiliates	21	19
Current Liabilities of Unconsolidated Affiliates	13	15
Non-current Liabilities of Unconsolidated Affiliates	$ 10	$ 10