Employee Retirement Plans (Net Periodic Benefit Expense) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 25	$ 26	$ 76	$ 77
Interest cost	37	32	111	97
Expected return on plan assets	(42)	(47)	(128)	(142)
Amortization of prior service cost (credit)	2	2	5	6
Recognition of actuarial loss			23	1
Total pension and postretirement benefit expense	22	13	87	39
Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	3	3	7	9
Interest cost	7	6	21	18
Amortization of actuarial net gain	(1)		(1)
Amortization of prior service cost (credit)	(2)	(2)	(6)	(5)
Total pension and postretirement benefit expense	$ 7	$ 7	$ 21	$ 22