INVESTMENT SECURITIES - Contractual Maturities (Details) $ in Millions	Sep. 30, 2020 USD ($)
Amortized cost
Within one year	$ 673
After one year through five years	2,568
After five years through ten years	6,516
After ten years	20,771
Estimated fair value
Within one year	684
After one year through five years	2,799
After five years through ten years	7,732
After ten years	$ 26,739