Pension and Other Postretirement Benefit Programs - Net Periodic Benefit Cost Relating to Pension and Other Postemployment Employee Benefit Plans (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Pension benefits
Net periodic benefit cost
Service cost	$ 20	$ 18	$ 61	$ 56
Interest cost	24	47	71	137
Expected return on plan assets	(40)	(74)	(121)	(214)
Amortization of net losses and prior service costs	19	15	57	44
Net periodic cost	23	6	68	23
OPEB
Net periodic benefit cost
Interest cost	2	2	4	6
Amortization of net losses and prior service costs	(5)	(7)	(13)	(21)
Net periodic cost	$ (3)	$ (5)	$ (9)	$ (15)