Lending Activities - Credit quality of residential mortgages (Details) - USD ($) $ in Millions	Mar. 31, 2023	Dec. 31, 2022
Financing Receivable, Credit Quality Indicator [Line Items]
Total	$ 51,616	$ 50,321
Residential mortgages
Financing Receivable, Credit Quality Indicator [Line Items]
Current year	413	997
Prior year	1,332	3,016
Two years prior	2,928	852
Three years prior	852	327
Four years prior	325	120
Five years & beyond prior	1,049	818
Total	6,899	6,130
780 and greater | Residential mortgages
Financing Receivable, Credit Quality Indicator [Line Items]
Current year	70	296
Prior year	539	2,204
Two years prior	2,328	654
Three years prior	649	232
Four years prior	234	77
Five years & beyond prior	637	567
Total	4,457	4,030
720 - 779 | Residential mortgages
Financing Receivable, Credit Quality Indicator [Line Items]
Current year	269	536
Prior year	541	728
Two years prior	511	168
Three years prior	168	76
Four years prior	71	32
Five years & beyond prior	234	169
Total	1,794	1,709
660 - 719 | Residential mortgages
Financing Receivable, Credit Quality Indicator [Line Items]
Current year	72	163
Prior year	231	80
Two years prior	82	28
Three years prior	34	16
Four years prior	16	9
Five years & beyond prior	104	62
Total	539	358
600 - 659 | Residential mortgages
Financing Receivable, Credit Quality Indicator [Line Items]
Current year	2	2
Prior year	21	4
Two years prior	6	2
Three years prior	1	2
Four years prior	2	2
Five years & beyond prior	50	14
Total	82	26
Less than 600 | Residential mortgages
Financing Receivable, Credit Quality Indicator [Line Items]
Current year	0	0
Prior year	0	0
Two years prior	1	0
Three years prior	0	1
Four years prior	2	0
Five years & beyond prior	24	6
Total	$ 27	$ 7