Employee Benefit Plans - Schedule of Effect of One-Percentage Point Change in Assumed Health Care Cost Trend Rate (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan, Effect of One-Percentage Point Change in Assumed Health Care Cost Trend Rate [Abstract]
Effect of one percentage point increase on accumulated postretirement benefit obligation	$ 3	$ 4
Effect of one percentage point decrease on accumulated postretirement benefit obligation	$ (3)	$ (4)

Amount of decrease in accumulated postretirement benefit obligation from one-percentage-point decrease in assumed health care cost trend rate.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (m)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

Name:	us-gaap_DefinedBenefitPlanEffectOfOnePercentagePointDecreaseOnAccumulatedPostretirementBenefitObligation1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration