Equity, Income Tax Effects on Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Other Comprehensive Income (Loss), before Tax
Other comprehensive income (loss) before income tax expense (benefit)		$ 449	$ (513)	$ (549)
Other Comprehensive Income (Loss), Tax
Income tax expense (benefit) related to items of other comprehensive income (loss)		(21)	(37)	17
Other Comprehensive Income (Loss), Net of Tax
Reclassification from accumulated other comprehensive income (loss), current period, net of tax		12	7	19
Other comprehensive income (loss)		470	(476)	(566)
Foreign Currency Translation Adjustment [Member]
Other Comprehensive Income (Loss), before Tax
Other comprehensive income (loss), before reclassifications, before tax		514	(415)	(606)
Other Comprehensive Income (Loss), Tax
Other comprehensive income (loss), before reclassifications, tax expense (benefit)		0	0	0
Other Comprehensive Income (Loss), Net of Tax
Other comprehensive income (loss), before reclassifications, net of tax		514	(415)	(606)
Net Actuarial Gain (Loss) [Member]
Other Comprehensive Income (Loss), before Tax
Other comprehensive income (loss), before reclassifications, before tax		(79)	(110)	50
Reclassification from accumulated other comprehensive income (loss), current period, before tax	[1]	50	48	62
Other Comprehensive Income (Loss), Tax
Other comprehensive income (loss), before reclassifications, tax expense (benefit)		(29)	(34)	15
Reclassification from accumulated other comprehensive income (loss), current period, tax expense (benefit)		18	18	22
Other Comprehensive Income (Loss), Net of Tax
Other comprehensive income (loss), before reclassifications, net of tax		(50)	(76)	35
Reclassification from accumulated other comprehensive income (loss), current period, net of tax		32	30	40
Prior Service (Cost) Credit [Member]
Other Comprehensive Income (Loss), before Tax
Other comprehensive income (loss), before reclassifications, before tax		(4)		(22)
Reclassification from accumulated other comprehensive income (loss), current period, before tax	[1]	(36)	(36)	(40)
Other Comprehensive Income (Loss), Tax
Other comprehensive income (loss), before reclassifications, tax expense (benefit)		(1)		(8)
Reclassification from accumulated other comprehensive income (loss), current period, tax expense (benefit)		(13)	(13)	(14)
Other Comprehensive Income (Loss), Net of Tax
Other comprehensive income (loss), before reclassifications, net of tax		(3)		(14)
Reclassification from accumulated other comprehensive income (loss), current period, net of tax		(23)	(23)	(26)
Miscellaneous Gain (Loss) [Member]
Other Comprehensive Income (Loss), before Tax
Other comprehensive income (loss), before reclassifications, before tax		0	0
Other Comprehensive Income (Loss), Tax
Other comprehensive income (loss), before reclassifications, tax expense (benefit)		3	(8)
Other Comprehensive Income (Loss), Net of Tax
Other comprehensive income (loss), before reclassifications, net of tax		(3)	8
Curtailment and Settlement Loss [Member]
Other Comprehensive Income (Loss), before Tax
Reclassification from accumulated other comprehensive income (loss), current period, before tax	[1]	4	0	7
Other Comprehensive Income (Loss), Tax
Reclassification from accumulated other comprehensive income (loss), current period, tax expense (benefit)		1		2
Other Comprehensive Income (Loss), Net of Tax
Reclassification from accumulated other comprehensive income (loss), current period, net of tax		3		5
Net Gain (Loss) on Pension and Other Postretirement Benefits [Member]
Other Comprehensive Income (Loss), before Tax
Reclassification from accumulated other comprehensive income (loss), current period, before tax		18	12	29
Other comprehensive income (loss) before income tax expense (benefit)		(65)	(98)	57
Other Comprehensive Income (Loss), Tax
Reclassification from accumulated other comprehensive income (loss), current period, tax expense (benefit)		6	5	10
Income tax expense (benefit) related to items of other comprehensive income (loss)		(21)	(37)	17
Other Comprehensive Income (Loss), Net of Tax
Other comprehensive income (loss)		$ (44)	$ (61)	$ 40

[1] These accumulated other comprehensive loss components are included in the computation of net periodic benefit cost, as further discussed in Note 12. Net periodic benefit cost is reflected in operating expenses (excluding depreciation and amortization expense) and general and administrative expenses (excluding depreciation and amortization expense).