Lending Activities - Credit quality of residential mortgages (Details) - Residential mortgages - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Financing Receivable, Credit Quality Indicator [Line Items]
Current year	$ 1,393	$ 997
Prior year	1,436	3,016
Two years prior	2,961	852
Three years prior	850	327
Four years prior	393	120
Five years & beyond prior	1,065	818
Total	8,098	6,130
780 and greater
Financing Receivable, Credit Quality Indicator [Line Items]
Current year	354	296
Prior year	568	2,204
Two years prior	2,296	654
Three years prior	630	232
Four years prior	242	77
Five years & beyond prior	618	567
Total	4,708	4,030
720 - 779
Financing Receivable, Credit Quality Indicator [Line Items]
Current year	822	536
Prior year	598	728
Two years prior	550	168
Three years prior	169	76
Four years prior	100	32
Five years & beyond prior	248	169
Total	2,487	1,709
660 - 719
Financing Receivable, Credit Quality Indicator [Line Items]
Current year	215	163
Prior year	249	80
Two years prior	103	28
Three years prior	40	16
Four years prior	38	9
Five years & beyond prior	130	62
Total	775	358
600 - 659
Financing Receivable, Credit Quality Indicator [Line Items]
Current year	2	2
Prior year	21	4
Two years prior	10	2
Three years prior	9	2
Four years prior	9	2
Five years & beyond prior	53	14
Total	104	26
Less than 600
Financing Receivable, Credit Quality Indicator [Line Items]
Current year	0	0
Prior year	0	0
Two years prior	2	0
Three years prior	2	1
Four years prior	4	0
Five years & beyond prior	16	6
Total	$ 24	$ 7