Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Accumulated Other Comprehensive Income Loss [Line Items]
Accumulated other comprehensive income, beginning balance		$ 7,017	$ 4,961
Other comprehensive income (loss) before reclassification, net of tax		1,335	412
Amounts reclassifed from accumulated OCI, net of tax		(311)	(213)
Net other comprehensive income (loss), net of tax		1,024	199
Amounts reclassifed to retained earnings		(655)
Accumulated other comprehensive income, ending balance		7,386	5,160
Foreign Currency Translation Adjustment [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Accumulated other comprehensive income, beginning balance		(2,054)	(1,995)
Other comprehensive income (loss) before reclassification, net of tax		106	366
Amounts reclassifed from accumulated OCI, net of tax	[1]	0	0
Net other comprehensive income (loss), net of tax		106	366
Amounts reclassifed to retained earnings		0
Accumulated other comprehensive income, ending balance		(1,948)	(1,629)
Net Unrealized Gains (Losses) on Available-for-Sale Securities [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Accumulated other comprehensive income, beginning balance		660	541
Other comprehensive income (loss) before reclassification, net of tax		(12)	33
Amounts reclassifed from accumulated OCI, net of tax	[1]	0	5
Net other comprehensive income (loss), net of tax		(12)	38
Amounts reclassifed to retained earnings	[2]	(655)
Accumulated other comprehensive income, ending balance		(7)	579
Net Unrealized Gains (Losses) on Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Accumulated other comprehensive income, beginning balance		1,402	744
Other comprehensive income (loss) before reclassification, net of tax		674	13
Amounts reclassifed from accumulated OCI, net of tax	[3]	12	10
Net other comprehensive income (loss), net of tax		686	23
Amounts reclassifed to retained earnings		0
Accumulated other comprehensive income, ending balance		2,088	767
Defined Benefit Postretirement Plans [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Accumulated other comprehensive income, beginning balance		7,009	5,671
Other comprehensive income (loss) before reclassification, net of tax		567	0
Amounts reclassifed from accumulated OCI, net of tax	[4]	(323)	(228)
Net other comprehensive income (loss), net of tax		244	(228)
Amounts reclassifed to retained earnings		0
Accumulated other comprehensive income, ending balance		$ 7,253	$ 5,443

[1] (Gains) losses are included in Other income (expense) - net in the consolidated statements of income.

[2] With the adoption of ASU 2016-01, the unrealized (gains) losses on our equity investments are reclassifed to retained earnings (see Note 1).

[3] (Gains) losses are included in Interest expense in the consolidated statements of income. See Note 7 for additional information.

[4] The amortization of prior service credits associated with postretirement benefits, net of amounts capitalized as part of construction labor, are included in Other income (expense) in the consolidated statements of income (see Note 5).