Note 10 - Employee Retirement Plans - Net Periodic Benefit Expense (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Pension Plan [Member]
Service cost	$ 32	$ 29	$ 64	$ 58
Interest cost	21	31	43	62
Expected return on plan assets	(54)	(49)	(108)	(98)
Amortization of prior service cost (credit)	1	2	2	3
Recognition of actuarial loss (gain)	10	(2)	10	(2)
Total pension and postretirement benefit expense	10	11	11	23
Other Postretirement Benefits Plan [Member]
Service cost	3	3	5	5
Interest cost	4	5	8	10
Expected return on plan assets
Amortization of prior service cost (credit)	(2)	(2)	(3)	(3)
Recognition of actuarial loss (gain)	1		1
Total pension and postretirement benefit expense	$ 6	$ 6	$ 11	$ 12