Note 10 - Employee Retirement Plans - Net Periodic Benefit Expense (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Pension Plan [Member]
Service cost	$ 32	$ 29	$ 96	$ 87
Interest cost	22	32	65	94
Expected return on plan assets	(54)	(49)	(162)	(147)
Amortization of prior service cost (credit)	1	1	3	4
Recognition of actuarial loss (gain)			10	(2)
Total pension and postretirement benefit expense	1	13	12	36
Other Postretirement Benefits Plan [Member]
Service cost	3	2	8	7
Interest cost	3	5	11	15
Amortization of prior service cost (credit)	(1)	(2)	(4)	(5)
Recognition of actuarial loss (gain)		1	1	1
Total pension and postretirement benefit expense	$ 5	$ 6	$ 16	$ 18