Benefit Obligations (Schedule of Net Periodic Benefit Costs Recognized) (Details) - USD ($) $ in Millions		3 Months Ended	12 Months Ended
		Dec. 31, 2013	Dec. 31, 2015		Dec. 31, 2014		Dec. 31, 2013
Defined Benefit Plan Disclosure [Line Items]
Recognized actuarial (gain) loss			$ 127		$ 350		$ (104)
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost			12		11		34
Interest cost			139		168		154
Expected return on plan assets			(209)		(214)		(223)
Amortization of prior service cost / (credit)			0		0		1
Recognized actuarial (gain) loss			134	[1]	339	[2]	(67)
Curtailment (gain) loss			(3)		0		(61)
Settlement (gain) loss			0		(78)		9
Special termination benefit			2		0		0
Total			75		226		(153)
Recognized actuarial (gain) loss relating to mortality table change	[1]		(62)		53
Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost			1		1		2
Interest cost			3		4		9
Expected return on plan assets			0		0		0
Amortization of prior service cost / (credit)			0		(83)		(12)
Recognized actuarial (gain) loss			(7)		11		(37)
Curtailment (gain) loss			0		0		0
Settlement (gain) loss			0		0		0
Special termination benefit			0		0		0
Total			$ (3)		(67)		$ (38)
UNITED STATES | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Curtailment (gain) loss		$ (61)
Settlement (gain) loss					(78)
UNITED STATES | Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Amortization of prior service cost / (credit)		$ (13)			$ (84)

[1] Includes a gain of $62 million reflecting the incorporation of the RP-2015

[2] Includes a loss of $53 million reflecting the incorporation of the RP-2014