Shareholders' Equity - Accumulated Other Comprehensive Income (Loss) - Components and Changes of Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated other comprehensive income (loss), net of tax, beginning balance	$ (2,548)	$ (2,283)
Other comprehensive income before reclassifications, net of taxes	115	63
Amounts reclassified into income, net of taxes	19	19
Accumulated other comprehensive income (loss), net of tax, ending balance	(2,414)	(2,202)
Foreign Currency Translation
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated other comprehensive income (loss), net of tax, beginning balance	(1,416)	(1,256)
Other comprehensive income before reclassifications, net of taxes	64	26
Amounts reclassified into income, net of taxes	0	0
Accumulated other comprehensive income (loss), net of tax, ending balance	(1,352)	(1,230)
Benefit Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated other comprehensive income (loss), net of tax, beginning balance	(1,040)	(1,005)
Other comprehensive income before reclassifications, net of taxes	24	0
Amounts reclassified into income, net of taxes	18	17
Accumulated other comprehensive income (loss), net of tax, ending balance	(998)	(988)
Cash Flow Hedges
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated other comprehensive income (loss), net of tax, beginning balance	(91)	(23)
Other comprehensive income before reclassifications, net of taxes	27	37
Amounts reclassified into income, net of taxes	2	2
Accumulated other comprehensive income (loss), net of tax, ending balance	$ (62)	$ 16