Investment securities (Investments Classified by Credit Rating) (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities	$ 4,680	$ 1,062
Agency mortgage-backed residential
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities	999	1,062
Mortgage-backed residential
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities	3,603	0
Asset-backed
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities	78	0
AAA
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities	3,570	0
AAA | Agency mortgage-backed residential
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities	0	0
AAA | Mortgage-backed residential
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities	3,497
AAA | Asset-backed
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities	73
AA
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities	1,094	1,062
AA | Agency mortgage-backed residential
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities	999	1,062
AA | Mortgage-backed residential
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities	93
AA | Asset-backed
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities	2
A
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities	15	0
A | Agency mortgage-backed residential
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities	0	0
A | Mortgage-backed residential
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities	13
A | Asset-backed
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities	2
BBB
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities	1	0
BBB | Agency mortgage-backed residential
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities	0	$ 0
BBB | Mortgage-backed residential
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities	0
BBB | Asset-backed
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities	$ 1