Future Policy Benefits (Assumption Explanations) (Details) - Other Segments - USD ($)	Sep. 30, 2024	Sep. 30, 2023
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	$ 12,500,000,000	$ 12,000,000,000
Future Policy Benefits Actual To Expected Variance	(113,000,000)	(5,000,000)
Impact Of Updating Discount Rate Recognized In OCI	(7,000,000)	1,000,000
Changes In Cash Flow Assumptions	31,000,000	17,000,000
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	3,400,000,000
Future Policy Benefits Actual To Expected Variance	(6,000,000)	(5,000,000)
Impact Of Updating Discount Rate Recognized In OCI	(134,000,000)	267,000,000
Changes In Cash Flow Assumptions	28,000,000	12,000,000
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	1,500,000,000	1,300,000,000
Future Policy Benefits Actual To Expected Variance	4,000,000	9,000,000
Impact Of Updating Discount Rate Recognized In OCI	109,000,000	88,000,000
Changes In Cash Flow Assumptions	25,000,000	47,000,000
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	4,900,000,000	4,500,000,000
Future Policy Benefits Actual To Expected Variance	89,000,000	(49,000,000)
Impact Of Updating Discount Rate Recognized In OCI	(171,000,000)	233,000,000
Changes In Cash Flow Assumptions	73,000,000	9,000,000
Insurance, Other | Americas [Member]
Liability for Future Policy Benefit, by Product Segment [Line Items]
Net Liability For Future Policy Benefits At Original Discount Rate	8,100,000,000	4,900,000,000
Future Policy Benefits Actual To Expected Variance	(3,000,000)	(8,000,000)
Impact Of Updating Discount Rate Recognized In OCI	(124,000,000)	(119,000,000)
Changes In Cash Flow Assumptions	8,000,000	22,000,000
Insurance, Other | CANADA
Liability for Future Policy Benefit, by Product Segment [Line Items]
Net Liability For Future Policy Benefits At Original Discount Rate	4,100,000,000	26,000,000,000
Future Policy Benefits Actual To Expected Variance	0	(8,000,000)
Impact Of Updating Discount Rate Recognized In OCI	(168,000,000)	(1,000,000)
Changes In Cash Flow Assumptions	0	22,000,000
Insurance, Other | EMEA [Member]
Liability for Future Policy Benefit, by Product Segment [Line Items]
Net Liability For Future Policy Benefits At Original Discount Rate	7,000,000,000	5,900,000,000
Future Policy Benefits Actual To Expected Variance	1,000,000	13,000,000,000
Impact Of Updating Discount Rate Recognized In OCI	241,000,000	67,000,000
Changes In Cash Flow Assumptions	3,000,000	34,000,000
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	12,700,000,000	5,700,000,000
Future Policy Benefits Actual To Expected Variance	1,000,000	2,000,000
Impact Of Updating Discount Rate Recognized In OCI	(540,000,000)	(359,000,000)
Changes In Cash Flow Assumptions	$ 9,000,000	$ 0