Debt (Detail) ¥ in Millions, $ in Millions	Sep. 30, 2025 USD ($)	Sep. 30, 2025 CNY (¥)	Aug. 31, 2025 USD ($)	Jul. 31, 2025 USD ($)	Jun. 30, 2025 USD ($)	Apr. 30, 2025 USD ($)
Group Syndicated Credit Facility
Debt Instrument [Line Items]
Line of Credit Facility, Current Borrowing Capacity	$ 3,000
INA Senior Notes Due March 2025 | Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount					$ 800
Debt Instrument, Interest Rate, Stated Percentage					3.15%
Commercial Paper Program | Commercial Paper
Debt Instrument [Line Items]
Line of Credit Facility, Current Borrowing Capacity	2,000
Senior Notes [Member] | INA Senior Notes Due August 2035 [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 1,250
Debt Instrument, Interest Rate, Stated Percentage	4.90%	4.90%
Make Whole Premium Additional Percent	0.15%	0.15%
Senior Notes [Member] | INA CNY Bond Due 2030 [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount		¥ 1,000	$ 139
Debt Instrument, Interest Rate, Stated Percentage	2.50%	2.50%
Senior Notes [Member] | INA CNY Bond Due 2035 [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount		¥ 1,500	209
Debt Instrument, Interest Rate, Stated Percentage	2.75%	2.75%
Senior Notes [Member] | INA CNY Bond Due 2055 [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount		¥ 2,000	$ 279
Debt Instrument, Interest Rate, Stated Percentage	3.05%	3.05%
Loans | INA CNH Term Loan Due April 2028 [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount		¥ 1,800				$ 249
Debt Instrument, Interest Rate, Stated Percentage	2.85%	2.85%
Loans | INA CNH Term Loan Due July 2028 [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount		¥ 2,100		$ 299
Debt Instrument, Interest Rate, Stated Percentage	2.75%	2.75%