Postretirement Plans Postretirement Plans Narrative (Details) $ in Millions	6 Months Ended
Jun. 30, 2017 USD ($)
Cash Contribution [Member]
Defined Contribution Plan Disclosure [Line Items]
Defined Benefit Plan, Expected Contributions in Current Fiscal Year	$ 500
Non-Cash Contribution [Member]
Defined Contribution Plan Disclosure [Line Items]
Defined Benefit Plan, Expected Contributions in Current Fiscal Year	$ 3,500

Amount of the employer's best estimate of contributions expected to be paid to the plan in the current fiscal period.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e2709-114920

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