Employee Benefit Plans (Accumulated Other Comprehensive Loss Pretax Amounts Not Yet Reflected in Net Periodic Benefit Cost) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
United States
Defined Benefit Plan Disclosure [Line Items]
Accumulated net actuarial losses	$ 800	$ 835
Accumulated prior service cost (credit)	2	0
Total	802	835
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Accumulated net actuarial losses	113	180
Accumulated prior service cost (credit)	(178)	(239)
Total	$ (65)	$ (59)