Note 10 - Employee Retirement Plans - Net Periodic Benefit Expense (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Pension Plan [Member]
Service cost	$ 32	$ 29
Interest cost	22	31
Expected return on plan assets	(54)	(49)
Amortization of prior service cost (credit)	1	1
Total pension and postretirement benefit expense	1	12
Other Postretirement Benefits Plan [Member]
Service cost	2	2
Interest cost	4	5
Amortization of prior service cost (credit)	(1)	(1)
Total pension and postretirement benefit expense	$ 5	$ 6