Benefit Plans (Components of Net Periodic Benefit Cost) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 208	[1]	$ 207	[1]	$ 205
Interest cost	108	[1]	146	[1]	156
Expected return on plan assets	(326)		(346)		(340)
Amortization:
Net losses	186		186		194
Prior service cost	6		4		4
Settlement and curtailment	6		4		3
Net periodic pension cost	188		201		222
Postretirement [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	4		3		4
Interest cost	8		9		9
Expected return on plan assets	0		0		0
Amortization:
Net losses	5		2		4
Prior service cost	0		0		0
Settlement and curtailment	0		0		0
Net periodic pension cost	$ 17		$ 14		$ 17

[1] Primarily non-U.S. based defined benefit retirement plans.