Income Taxes - Other (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Liability for unrecognized tax benefits	$ 23	$ 23
Decrease in unrecognized tax benefits is reasonably possible	$ 3

Amount of decrease reasonably possible in the next twelve months for the unrecognized tax benefit.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (d)(3)
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32718-109319

Name:	us-gaap_DecreaseInUnrecognizedTaxBenefitsIsReasonablyPossible
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant