Equity Changes in Accumulated Other Comprehensive Loss, Net of Tax (Details) - USD ($) $ in Millions		12 Months Ended
		Sep. 28, 2019	Sep. 29, 2018	Sep. 30, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax		$ (3,097)	$ (3,528)	$ (3,979)
Unrealized gains (losses) arising during the period		(2,886)	130	318
Reclassifications of realized net (gains) losses to net income		72	301	133
AOCI reclassifications to retained earnings, net of tax	[1]	(706)
Accumulated Other Comprehensive Income (Loss), Net of Tax		(6,617)	(3,097)	(3,528)
Market Value Adjustments, Investments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax		15	8	26
Unrealized gains (losses) arising during the period		(2)	7	(1)
Reclassifications of realized net (gains) losses to net income		0	0	(17)
AOCI reclassifications to retained earnings, net of tax	[1]	(15)
Accumulated Other Comprehensive Income (Loss), Net of Tax		(2)	15	8
Market Value Adjustments, Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax		145	(62)	(25)
Unrealized gains (losses) arising during the period		107	184	85
Reclassifications of realized net (gains) losses to net income		(142)	23	(122)
AOCI reclassifications to retained earnings, net of tax	[1]	(8)
Accumulated Other Comprehensive Income (Loss), Net of Tax		102	145	(62)
Unrecognized Pension and Postretirement Medical Expense
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax		(2,633)	(3,067)	(3,651)
Unrealized gains (losses) arising during the period		(2,660)	156	312
Reclassifications of realized net (gains) losses to net income		214	278	272
AOCI reclassifications to retained earnings, net of tax	[1]	(667)
Accumulated Other Comprehensive Income (Loss), Net of Tax		(5,746)	(2,633)	(3,067)
Foreign Currency Translation and Other
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax		(624)	(407)	(329)
Unrealized gains (losses) arising during the period		(331)	(217)	(78)
Reclassifications of realized net (gains) losses to net income		0	0	0
AOCI reclassifications to retained earnings, net of tax	[1]	(16)
Accumulated Other Comprehensive Income (Loss), Net of Tax		$ (971)	$ (624)	$ (407)

[1] At the beginning of fiscal 2019, the Company adopted new FASB accounting guidance, Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income, and reclassified $691 million from AOCI to retained earnings. In addition, at the beginning of fiscal 2019, the Company adopted new FASB accounting guidance, Recognition and Measurement of Financial Assets and Liabilities, and reclassified $24 million ($15 million after tax) of market value adjustments on investments previously recorded in AOCI to retained earnings.