Employee Benefit Plans (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Employee Benefit Plans [Abstract]
Interest cost	$ (32)	$ (34)	$ (64)	$ (68)
Expected return on plan assets	52	47	104	94
Net periodic pension benefit	$ 20	$ 13	$ 40	$ 26