Settlement Guarantee Management - Collateral (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Sep. 30, 2019
Settlement Guarantee Management [Abstract]
Restricted cash and restricted cash equivalents	$ 1,698	$ 1,648
Pledged securities at market value	241	259
Letters of credit	1,325	1,293
Guarantees	506	477
Total	$ 3,770	$ 3,677