Employee Benefit Plans (Accumulated Other Comprehensive Loss Pretax Amounts Not Yet Reflected in Net Periodic Benefit Cost) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Total	$ 2,561	$ 4,627
Pensions
Defined Benefit Plan Disclosure [Line Items]
Accumulated net actuarial losses	918	1,872
Accumulated prior service cost (credit)	1	(18)
Total	919	1,854
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Accumulated net actuarial losses	226	228
Accumulated prior service cost (credit)	(298)	(24)
Total	$ (72)	$ 204