Investment securities (Investments Classified by Credit Rating) (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities	$ 1,013	$ 1,062
Agency mortgage-backed security
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities	1,013	1,062
AA
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities	1,013	1,062
AA | Agency mortgage-backed security
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities	$ 1,013	$ 1,062