Guarantees and Contingent Liabilities - Summary of Other Guarantees and Contingent Liabilities (Detail) $ in Millions	Sep. 30, 2015 USD ($)
Standby Letters of Credit [Member]
Guarantor Obligations [Line Items]
Collateral Held
Carrying Amount	$ 54
Maximum Potential Future Payments	$ 13,336
Third Party Borrowing Arrangements [Member]
Guarantor Obligations [Line Items]
Collateral Held
Carrying Amount
Maximum Potential Future Payments	$ 12
Securities Lending Indemnifications [Member]
Guarantor Obligations [Line Items]
Collateral Held	$ 5,980
Carrying Amount
Maximum Potential Future Payments	$ 5,877
Asset Sales [Member]
Guarantor Obligations [Line Items]
Collateral Held
Carrying Amount	$ 133
Maximum Potential Future Payments	4,908
Merchant Processing [Member]
Guarantor Obligations [Line Items]
Collateral Held	545
Carrying Amount	59
Maximum Potential Future Payments	$ 100,063
Contingent Consideration Arrangements [Member]
Guarantor Obligations [Line Items]
Collateral Held
Carrying Amount	$ 2
Maximum Potential Future Payments	2
Tender Option Bond Program Guarantee [Member]
Guarantor Obligations [Line Items]
Collateral Held	$ 2,276
Carrying Amount
Maximum Potential Future Payments	$ 2,184
Minimum Revenue Guarantees [Member]
Guarantor Obligations [Line Items]
Collateral Held
Carrying Amount	$ 2
Maximum Potential Future Payments	$ 12
Other Guarantees [Member]
Guarantor Obligations [Line Items]
Collateral Held
Carrying Amount
Maximum Potential Future Payments	$ 769