Lending Activities - Credit quality of residential mortgages (Details) - Residential mortgages - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Financing Receivable, Credit Quality Indicator [Line Items]
Current year	$ 1,950	$ 997
Prior year	1,492	3,016
Two years prior	2,969	852
Three years prior	841	327
Four years prior	389	120
Five years & beyond prior	1,048	818
Total	8,689	6,130
780 and greater
Financing Receivable, Credit Quality Indicator [Line Items]
Current year	514	296
Prior year	589	2,204
Two years prior	2,283	654
Three years prior	622	232
Four years prior	240	77
Five years & beyond prior	608	567
Total	4,856	4,030
720 - 779
Financing Receivable, Credit Quality Indicator [Line Items]
Current year	1,121	536
Prior year	625	728
Two years prior	560	168
Three years prior	169	76
Four years prior	99	32
Five years & beyond prior	243	169
Total	2,817	1,709
660 - 719
Financing Receivable, Credit Quality Indicator [Line Items]
Current year	313	163
Prior year	257	80
Two years prior	113	28
Three years prior	40	16
Four years prior	37	9
Five years & beyond prior	128	62
Total	888	358
600 - 659
Financing Receivable, Credit Quality Indicator [Line Items]
Current year	2	2
Prior year	20	4
Two years prior	11	2
Three years prior	8	2
Four years prior	9	2
Five years & beyond prior	53	14
Total	103	26
Less than 600
Financing Receivable, Credit Quality Indicator [Line Items]
Current year	0	0
Prior year	1	0
Two years prior	2	0
Three years prior	2	1
Four years prior	4	0
Five years & beyond prior	16	6
Total	$ 25	$ 7