Investment securities (Investments Classified by Credit Rating) (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities	$ 4,655	$ 4,680
Agency mortgage-backed residential
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities	984	999
Mortgage-backed residential
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities	3,544	3,603
Asset-backed
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities	127	78
AAA
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities	3,560	3,570
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	3,442	3,497
AAA | Asset-backed
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities	118	73
AA
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities	1,077	1,094
AA | Agency mortgage-backed residential
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities	984	999
AA | Mortgage-backed residential
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities	89	93
AA | Asset-backed
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities	4	2
A
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities	16	15
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	13
A | Asset-backed
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities	3	2
BBB
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities	2	1
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	0
BBB | Asset-backed
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities	$ 2	$ 1