Future Policy Benefits (Assumption Explanations) (Details) - Other Segments - USD ($)	Sep. 30, 2025	Sep. 30, 2024
Life Insurance Product Line [Member] \| Americas [Member]
Liability for Future Policy Benefit, by Product Segment [Line Items]
Net Liability For Future Policy Benefits At Original Discount Rate	$ 15,400,000,000	$ 12,500,000,000
Future Policy Benefits Actual To Expected Variance	(61,000,000)	(113,000,000)
Impact Of Updating Discount Rate Recognized In OCI	(375,000,000)	7,000,000
Changes In Cash Flow Assumptions	29,000,000	31,000,000
Life Insurance Product Line [Member] \| CANADA
Liability for Future Policy Benefit, by Product Segment [Line Items]
Net Liability For Future Policy Benefits At Original Discount Rate	3,600,000,000	3,600,000,000
Future Policy Benefits Actual To Expected Variance	(3,000,000)	(6,000,000)
Impact Of Updating Discount Rate Recognized In OCI	(152,000,000)	134,000,000
Changes In Cash Flow Assumptions	9,000,000	28,000,000
Life Insurance Product Line [Member] \| EMEA [Member]
Liability for Future Policy Benefit, by Product Segment [Line Items]
Net Liability For Future Policy Benefits At Original Discount Rate	1,900,000,000	1,500,000,000
Future Policy Benefits Actual To Expected Variance	10,000,000	4,000,000
Impact Of Updating Discount Rate Recognized In OCI	243,000,000	109,000,000
Changes In Cash Flow Assumptions	223,000,000	25,000,000
Life Insurance Product Line [Member] \| Asia Pacific [Member]
Liability for Future Policy Benefit, by Product Segment [Line Items]
Net Liability For Future Policy Benefits At Original Discount Rate	5,300,000,000	4,900,000,000
Future Policy Benefits Actual To Expected Variance	65,000,000	(89,000,000)
Impact Of Updating Discount Rate Recognized In OCI	(49,000,000)	171,000,000
Changes In Cash Flow Assumptions	2,000,000	73,000,000
Insurance, Other \| Americas [Member]
Liability for Future Policy Benefit, by Product Segment [Line Items]
Net Liability For Future Policy Benefits At Original Discount Rate	10,000,000,000	8,100,000,000
Future Policy Benefits Actual To Expected Variance	(3,000,000)	(3,000,000)
Impact Of Updating Discount Rate Recognized In OCI	(260,000,000)	(124,000,000)
Changes In Cash Flow Assumptions	0	8,000,000
Insurance, Other \| CANADA
Liability for Future Policy Benefit, by Product Segment [Line Items]
Net Liability For Future Policy Benefits At Original Discount Rate	4,600,000,000	4,100,000,000
Future Policy Benefits Actual To Expected Variance	0	0
Impact Of Updating Discount Rate Recognized In OCI	(135,000,000)	(168,000,000)
Changes In Cash Flow Assumptions	0	0
Insurance, Other \| EMEA [Member]
Liability for Future Policy Benefit, by Product Segment [Line Items]
Net Liability For Future Policy Benefits At Original Discount Rate	10,100,000,000	7,000,000,000
Future Policy Benefits Actual To Expected Variance	19,000,000	1,000,000
Impact Of Updating Discount Rate Recognized In OCI	128,000,000	241,000,000
Changes In Cash Flow Assumptions	24,000,000	3,000,000
Insurance, Other \| Asia Pacific [Member]
Liability for Future Policy Benefit, by Product Segment [Line Items]
Net Liability For Future Policy Benefits At Original Discount Rate	15,500,000,000	12,700,000,000
Future Policy Benefits Actual To Expected Variance	6,000,000	1,000,000
Impact Of Updating Discount Rate Recognized In OCI	(1,500,000)	(540,000,000)
Changes In Cash Flow Assumptions	$ 0	$ 9,000,000

Future Policy Benefits (Assumption Explanations) (Details) - Other Segments - USD ($)

Sep. 30, 2025

Sep. 30, 2024

Life Insurance Product Line [Member] | Americas [Member]

Liability for Future Policy Benefit, by Product Segment [Line Items]

Net Liability For Future Policy Benefits At Original Discount Rate

$ 15,400,000,000

$ 12,500,000,000

Future Policy Benefits Actual To Expected Variance

(61,000,000)

(113,000,000)

Impact Of Updating Discount Rate Recognized In OCI