Employee Benefit Plans (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Employee Benefit Plans [Abstract]
Discount Rate (percentage)			4.24%	3.88%	3.68%	4.20%
Expected long-term rate of return on plan assets (percentage)			5.75%		6.50%
Interest cost	$ (32)	$ (33)	$ (96)	$ (101)
Expected return on plan assets	52	46	156	140
Remeasurement gain (loss), net	187	(30)	187	(30)
Net periodic pension benefit (costs)	$ 207	$ (17)	$ 247	$ 9