Note 8 - Retirement Plans (Details Textual) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)
Capital Accumulation Plan [Member]
Defined Contribution Plan, Employer Discretionary Contribution Amount	$ 3	$ 7
Defined Benefit Plan, Expected Future Employer Contributions, Remainder of Fiscal Year	6	6
Pension Plan [Member] \| Gray Pension Plan [Member]
Defined Benefit Plan, Expected Future Employer Contributions, Remainder of Fiscal Year	$ 3	$ 3

Amount of contributions expected to be received by defined benefit plan from employer in fiscal year. Excludes contributions paid by employer in current fiscal year.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 6
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e2709-114920

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