Equity, Income Tax Effects on Other Comprehensive Income (Loss) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Effects Related to Components of Other Comprehensive Income (Loss)
Foreign currency translation adjustment, before-tax amount	$ (407)	$ (98)	$ 164
Pension and other postretirement benefits:
Net actuarial gain (loss) arising during the year, before-tax amount	(471)	367	(228)
Plan amendments, before tax amount		371
Prior service cost arising during the year, before tax amount	(1)		(9)
(Gain) loss reclassified into income related to:
Net actuarial loss, before-tax amount	34	57	34
Prior service credit, before-tax amount	(40)	(33)	(20)
Curtailment and settlement, before-tax amount	3	1	12
Net gain (loss) on pension and other postretirement benefits, before-tax amount	(475)	763	(211)
Derivative instruments designated and qualifying as cash flow hedges:
Net gain (loss) arising during the year, before-tax amount	(1)	(4)	45
Net (gain) loss reclassified into income, before-tax amount	2	2	(73)
Net gain (loss) on cash flow hedges, before-tax amount	1	(2)	(28)
Other comprehensive income (loss) before income tax expense (benefit)	(881)	663	(75)
Foreign currency translation adjustment, tax expense (benefit)	0	0	0
Pension and other postretirement benefits:
Net actuarial gain (loss) arising during the year, tax expense (benefit)	(162)	125	(79)
Plan amendments, tax expense		130
Prior service cost arising during the year, tax benefit	(1)		(3)
(Gain) loss reclassified into income related to:
Net actuarial loss, tax expense	12	20	12
Prior service credit, tax benefit	(14)	(12)	(7)
Curtailment and settlement, tax expense (benefit)	0	0	0
Net gain (loss) on pension and other postretirement benefits, tax expense (benefit)	(165)	263	(77)
Derivative instruments designated and qualifying as cash flow hedges:
Net gain (loss) arising during the year, tax expense (benefit)	0	(2)	16
Net (gain) loss reclassified into income, tax expense (benefit)	1	1	(26)
Net gain (loss) on cash flow hedges, tax expense (benefit)	1	(1)	(10)
Other comprehensive income (loss), tax expense (benefit)	(164)	262	(87)
Foreign currency translation adjustment, net	(407)	(98)	164
Pension and other postretirement benefits:
Net actuarial gain (loss) arising during the year, net	(309)	242	(149)
Plan amendments, net		241
Prior service cost arising during the year, net	0		(6)
(Gain) loss reclassified into income related to:
Net actuarial loss, net	22	37	22
Prior service credit, net	(26)	(21)	(13)
Curtailment and settlement, net	3	1	12
Net gain (loss) on pension and other postretirement benefits, net	(310)	500	(134)
Derivative instruments designated and qualifying as cash flow hedges:
Net gain (loss) arising during the year, net	(1)	(2)	29
Net (gain) loss reclassified into income, net	1	1	(47)
Net gain (loss) on cash flow hedges, net	0	(1)	(18)
Other comprehensive income (loss)	$ (717)	$ 401	$ 12