Retirement and Employee Benefit Plans (One Percentage Point Change in Assumed Health Care Cost Trend Rates) (Details) $ in Millions	12 Months Ended
Dec. 31, 2018 USD ($)
Retirement and Employee Benefit Plans [Abstract]
Effect on postretirement benefit obligations, 1% Increase	$ 2
Effect on postretirement benefit obligation, 1% Decrease	$ (1)

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

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (m)
-URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920

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