Supplemental Equity and Comprehensive Income Information - AOCI rf (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Stockholders' Equity Attributable to Parent, Beginning Balance	$ 11,708
Other comprehensive income (loss), before tax:
Stockholders' Equity Attributable to Parent, Ending Balance	11,733
Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Stockholders' Equity Attributable to Parent, Beginning Balance	(6,359)	$ (6,289)
Other comprehensive income (loss), before tax:
Amounts before reclassifications	(61)	116
Amounts reclassified out	51	97
Total other comprehensive income (loss), before tax	(10)	213
Tax effect	108	(245)
Total other comprehensive income (loss), net of tax	98	(32)
Stockholders' Equity Attributable to Parent, Ending Balance	(6,261)	(6,321)
Cumulative Translation Adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Stockholders' Equity Attributable to Parent, Beginning Balance	(1,679)	(1,095)
Other comprehensive income (loss), before tax:
Amounts before reclassifications	60	(44)
Total other comprehensive income (loss), before tax	60	(44)
Tax effect	79	(149)
Total other comprehensive income (loss), net of tax	139	(193)
Stockholders' Equity Attributable to Parent, Ending Balance	(1,540)	(1,288)
Gains (losses) associated with defined benefit pension and postretirement plans amortization
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Stockholders' Equity Attributable to Parent, Beginning Balance	(4,804)	(5,293)
Other comprehensive income (loss), before tax:
Amounts before reclassifications		24
Amounts reclassified out	103	124
Total other comprehensive income (loss), before tax	103	148
Tax effect	(34)	(57)
Total other comprehensive income (loss), net of tax	69	91
Stockholders' Equity Attributable to Parent, Ending Balance	(4,735)	(5,202)
Cash flow hedging instruments gains (losses)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Stockholders' Equity Attributable to Parent, Beginning Balance	124	99
Other comprehensive income (loss), before tax:
Amounts before reclassifications	(121)	136
Amounts reclassified out	(52)	(27)
Total other comprehensive income (loss), before tax	(173)	109
Tax effect	63	(39)
Total other comprehensive income (loss), net of tax	(110)	70
Stockholders' Equity Attributable to Parent, Ending Balance	$ 14	$ 169