Employee Retirement Plans (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 26	$ 26	$ 51	$ 51
Interest cost	37	33	74	65
Expected return on plan assets	(43)	(48)	(86)	(95)
Amortization of prior service cost (credit)	1	2	3	4
Recognition of actuarial loss	23	1	23	1
Total pension and postretirement benefit expense	44	14	65	26
Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	2	3	4	6
Interest cost	7	6	14	12
Amortization of prior service cost (credit)	(2)	(2)	(4)	(3)
Total pension and postretirement benefit expense	$ 7	$ 7	$ 14	$ 15