Equity and Accumulated Other Comprehensive Income - Changes in AOCI (Detail) - USD ($) $ in Millions	9 Months Ended
Sep. 30, 2018	Dec. 31, 2017
AOCI Including Portion Attributable to Noncontrolling Interest [Abstract]
Beginning Balance	$ 44,687
Opening balance sheet adjustment related to adoption of Topic 606, ASU 2018-02 and other ASUs (Note 1)		$ 2,906
Adjusted Beginning Balance		47,593
Other comprehensive income (loss)	(13)
Amounts reclassified to net income	(75)
Net other comprehensive income (loss)	(88)
Ending Balance	56,087
Foreign currency translation adjustments
AOCI Including Portion Attributable to Noncontrolling Interest [Abstract]
Beginning Balance	(468)
Opening balance sheet adjustment related to adoption of Topic 606, ASU 2018-02 and other ASUs (Note 1)		(15)
Adjusted Beginning Balance		(483)
Other comprehensive income (loss)	(65)
Amounts reclassified to net income	(8)
Net other comprehensive income (loss)	(73)
Ending Balance	(556)
Unrealized gain (loss) on cash flow hedges
AOCI Including Portion Attributable to Noncontrolling Interest [Abstract]
Beginning Balance	(111)
Opening balance sheet adjustment related to adoption of Topic 606, ASU 2018-02 and other ASUs (Note 1)		(24)
Adjusted Beginning Balance		(135)
Other comprehensive income (loss)	226
Amounts reclassified to net income	452
Net other comprehensive income (loss)	678
Ending Balance	543
Unrealized gain (loss) on marketable securities
AOCI Including Portion Attributable to Noncontrolling Interest [Abstract]
Beginning Balance	32
Opening balance sheet adjustment related to adoption of Topic 606, ASU 2018-02 and other ASUs (Note 1)		(13)
Adjusted Beginning Balance		19
Other comprehensive income (loss)	(5)
Amounts reclassified to net income	0
Net other comprehensive income (loss)	(5)
Ending Balance	14
Defined benefit pension and postretirement plans
AOCI Including Portion Attributable to Noncontrolling Interest [Abstract]
Beginning Balance	3,206
Opening balance sheet adjustment related to adoption of Topic 606, ASU 2018-02 and other ASUs (Note 1)		682
Adjusted Beginning Balance		3,888
Other comprehensive income (loss)	(169)
Amounts reclassified to net income	(519)
Net other comprehensive income (loss)	(688)
Ending Balance	3,200
Accumulated Other Comprehensive Income
AOCI Including Portion Attributable to Noncontrolling Interest [Abstract]
Beginning Balance	2,659
Opening balance sheet adjustment related to adoption of Topic 606, ASU 2018-02 and other ASUs (Note 1)		630
Adjusted Beginning Balance		$ 3,289
Ending Balance	$ 3,201

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