Employee Retirement Plans (Net Periodic Benefit Cost of Postretirement Benefits) (Details) - Postretirement Benefits [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 10	$ 10	$ 9
Interest cost	24	26	26
Amortization of actuarial net gain		(1)	(1)
Amortization of prior service credit	(7)	(3)	(4)
Total net periodic benefit expense	27	32	30
Current year actuarial loss (gain)	(47)	17	15
Amortization of actuarial net gain		1	1
Current year prior service cost/credit	(40)
Amortization of prior service (cost) credit	7	3	5
Total recognized in other comprehensive loss (income)	(80)	21	21
Total recognized in net periodic benefit cost and other comprehensive income	$ (53)	$ 53	$ 51