Equity Changes in Accumulated Other Comprehensive Loss, Tax (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2018	Apr. 01, 2017	Mar. 31, 2018	Apr. 01, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
AOCI Tax, Attributable to Parent, Beginning Balance	$ 1,922	$ 2,134	$ 1,994	$ 2,395
Other Comprehensive Income (Loss) before Reclassifications, Tax	(14)	73	(43)	(174)
Reclassification from AOCI, Current Period, Tax	(32)	(19)	(75)	(33)
AOCI Tax, Attributable to Parent, Ending Balance	1,876	2,188	1,876	2,188
Investments
Accumulated Other Comprehensive Income (Loss) [Line Items]
AOCI Tax, Attributable to Parent, Beginning Balance	(7)	(11)	(7)	(18)
Other Comprehensive Income (Loss) before Reclassifications, Tax	(3)	(3)	(3)	4
Reclassification from AOCI, Current Period, Tax	0	2	0	2
AOCI Tax, Attributable to Parent, Ending Balance	(10)	(12)	(10)	(12)
Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss) [Line Items]
AOCI Tax, Attributable to Parent, Beginning Balance	25	(143)	46	13
Other Comprehensive Income (Loss) before Reclassifications, Tax	25	74	12	(108)
Reclassification from AOCI, Current Period, Tax	(9)	19	(17)	45
AOCI Tax, Attributable to Parent, Ending Balance	41	(50)	41	(50)
Unrecognized Pension and Postretirement Medical Expense
Accumulated Other Comprehensive Income (Loss) [Line Items]
AOCI Tax, Attributable to Parent, Beginning Balance	1,804	2,146	1,839	2,208
Other Comprehensive Income (Loss) before Reclassifications, Tax	(3)	7	(3)	(15)
Reclassification from AOCI, Current Period, Tax	(23)	(40)	(58)	(80)
AOCI Tax, Attributable to Parent, Ending Balance	1,778	2,113	1,778	2,113
Foreign Currency Translation and Other
Accumulated Other Comprehensive Income (Loss) [Line Items]
AOCI Tax, Attributable to Parent, Beginning Balance	100	142	116	192
Other Comprehensive Income (Loss) before Reclassifications, Tax	(33)	(5)	(49)	(55)
Reclassification from AOCI, Current Period, Tax	0	0	0	0
AOCI Tax, Attributable to Parent, Ending Balance	$ 67	$ 137	$ 67	$ 137