SEGMENT INFORMATION, Classified by Major Geographic Areas (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2020	Dec. 31, 2019	Sep. 30, 2020
Revenues:
Total net revenues		$ 2,222	$ 2,009
Pre-tax income
Total pre-tax income		399	359
Total assets:
Total assets	$ 53,657	53,657		$ 47,482
Goodwill:
Goodwill	606	606		466
NWPS
Goodwill:
Goodwill, acquired during period	139
U.S.
Revenues:
Total net revenues		2,079	1,875
Pre-tax income
Total pre-tax income		396	352
Total assets:
Total assets	50,158	50,158		44,090
Goodwill:
Goodwill	572	572		433
U.S. | NWPS
Goodwill:
Goodwill, acquired during period		139
Canada
Revenues:
Total net revenues		105	95
Pre-tax income
Total pre-tax income		1	8
Total assets:
Total assets	3,380	3,380		3,260
Goodwill:
Goodwill	25	25		24
Europe
Revenues:
Total net revenues		38	39
Pre-tax income
Total pre-tax income		2	$ (1)
Total assets:
Total assets	119	119		132
Goodwill:
Goodwill	$ 9	$ 9		$ 9