Pension and Other Postretirement Benefit Plans (Components of Net Periodic Benefit Cost) (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended			81 Months Ended
	Sep. 30, 2015	Mar. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2017
Amortization:
Curtailment gain	$ (16)	$ (47)	$ 0	$ 0	$ (63)
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost			7	7	2
Interest cost			16	18	19
Expected return on plan assets			0	0	0
Amortization:
Actuarial loss			0	0	0
Prior service cost (credit)			(4)	(15)	(23)
Special termination benefit			4	0	0
Curtailment gain			0	0	(63)
Settlement loss			0	0	0
Net periodic benefit cost			23	10	(65)	$ (92)
United States Pension Benefits | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost			2	3	3
Interest cost			134	147	150
Expected return on plan assets			(175)	(186)	(191)
Amortization:
Actuarial loss			50	46	53
Prior service cost (credit)			(3)	(3)	(3)
Special termination benefit			0	0	0
Curtailment gain			0	4	0
Settlement loss			0	0	0
Net periodic benefit cost			8	11	12
Foreign Pension Benefits | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost			5	5	5
Interest cost			23	27	31
Expected return on plan assets			(30)	(30)	(33)
Amortization:
Actuarial loss			6	4	5
Prior service cost (credit)			0	0	0
Special termination benefit			0	0	0
Curtailment gain			0	(1)	0
Settlement loss			2	3	12
Net periodic benefit cost			6	8	20
Operating Income (Loss) | Other Postretirement Benefits
Amortization:
Net periodic benefit cost			7	7	2
Operating Income (Loss) | United States Pension Benefits | Pension Benefits
Amortization:
Net periodic benefit cost			2	3	3
Operating Income (Loss) | Foreign Pension Benefits | Pension Benefits
Amortization:
Net periodic benefit cost			5	5	5
Nonoperating Income (Expense) | Other Postretirement Benefits
Amortization:
Net periodic benefit cost			16	3	(67)
Nonoperating Income (Expense) | United States Pension Benefits | Pension Benefits
Amortization:
Net periodic benefit cost			6	8	9
Nonoperating Income (Expense) | Foreign Pension Benefits | Pension Benefits
Amortization:
Net periodic benefit cost			$ 1	$ 3	$ 15