Derivative instruments - Offsetting (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Derivative Asset
Derivatives subject to netting arrangements, Gross assets recognized	$ 8,446	$ 10,102
Total derivatives subject to netting arrangements, Gross amounts offset in the balance sheet	5,875	8,346
Derivatives subject to netting arrangements, Net assets recognized in the balance sheet	2,571	1,756
Total derivatives, Gross amounts not offset in the balance sheet, Financial instruments	317	457
Total derivatives, Gross amounts not offset in the balance sheet, Cash collateral received	0	0
Derivative assets subject to netting arrangements, Net amount	2,254	1,299
Total derivatives not subject to netting arrangements	1,832	2,089
Total derivatives, Gross assets recognized	10,278	12,191
Fair value after effect of master netting agreements	4,403	3,845
Total derivatives, Net amount	4,086	3,388
Reverse repurchase agreements, Gross assets recognized	66,757	78,828
Reverse repurchase agreements, Gross amounts offset in the balance sheet	49,195	59,561
Reverse repurchase agreements, Net assets recognized on the balance sheet	17,562	19,267
Reverse repurchase agreements, Gross amounts not offset in the balance sheet, Financial instruments	17,536	19,252
Reverse repurchase agreements, Gross amounts not offset in the balance sheet, Cash collateral received	0	0
Reverse repurchase agreements, Net amount	26	15
Securities borrowing, Gross assets recognized	10,935	11,640
Securities borrowing, Net assets recognized on the balance sheet	10,935	11,640
Securities borrowing, Gross amounts not offset in the balance sheet, Financial instruments	10,355	11,166
Securities borrowing, Net amount	580	474
Total, Gross assets recognized	87,970	102,659
Total, Gross amounts offset in the balance sheet	55,070	67,907
Total, Net assets recognized on the balance sheet	32,900	34,752
Total, Gross amounts not offset in the balance sheet, Financial instruments	28,208	30,875
Total, Gross amounts not offset in the balance sheet, Cash collateral received	0	0
Total, Net amount	4,692	3,877
Derivative Liability
Derivatives subject to netting arrangements, Gross liabilities recognized	9,142	11,850
Derivatives subject to netting arrangements, Gross amounts offset in the balance sheet	6,529	7,845
Derivatives subject to netting arrangements, Net liabilities recognized in the balance sheet	2,613	4,005
Total derivatives, Gross amounts not offset in the balance sheet, Financial instruments	1,750	2,265
Total derivatives, Gross amounts not offset in the balance sheet, Cash collateral pledged	0	0
Derivative liabilities subject to netting arrangements, Net amount	863	1,740
Total derivatives not subject to netting arrangements	507	800
Total derivatives, Gross liabilities recognized	9,649	12,650
Fair value after effect of master netting agreements	3,120	4,805
Total derivatives, Net amount	1,370	2,540
Repurchase agreements, Gross liabilities recognized	59,510	69,831
Repurchase agreements, Gross amounts offset in the balance sheet	49,195	59,561
Repurchase agreements, Net liabilities recognized on the balance sheet	10,315	10,270
Repurchase agreements, Gross amounts not offset in the balance sheet, Financial instruments	10,308	10,270
Repurchase agreements, Gross amounts not offset in the balance sheet, Cash collateral pledged	2	0
Repurchase agreements, Net amount	5	0
Securities lending, Gross liabilities recognized	1,658	1,035
Securities lending, Net liabilities recognized on the balance sheet	1,658	1,035
Securities lending, Gross amounts not offset in the balance sheet, Financial instruments	1,581	983
Securities lending, Net amount	77	52
Total, Gross liabilities recognized	70,817	83,516
Total, Gross amounts offset in the balance sheet	55,724	67,406
Total, Net liabilities recognized on the balance sheet	15,093	16,110
Total, Gross amounts not offset in the balance sheet, Financial instruments	13,639	13,518
Total, Gross amounts not offset in the balance sheet, Cash collateral pledged	2	0
Total, Net amount	1,452	2,592
Interest rate contracts
Derivative Asset
Derivatives subject to netting arrangements, Gross assets recognized	2,238	2,972
Total derivatives subject to netting arrangements, Gross amounts offset in the balance sheet	1,456	1,952
Derivatives subject to netting arrangements, Net assets recognized in the balance sheet	782	1,020
Total derivatives, Gross amounts not offset in the balance sheet, Financial instruments	223	311
Total derivatives, Gross amounts not offset in the balance sheet, Cash collateral received	0	0
Derivative assets subject to netting arrangements, Net amount	559	709
Derivative Liability
Derivatives subject to netting arrangements, Gross liabilities recognized	3,389	4,533
Derivatives subject to netting arrangements, Gross amounts offset in the balance sheet	1,844	2,348
Derivatives subject to netting arrangements, Net liabilities recognized in the balance sheet	1,545	2,185
Total derivatives, Gross amounts not offset in the balance sheet, Financial instruments	1,503	2,115
Total derivatives, Gross amounts not offset in the balance sheet, Cash collateral pledged	0	0
Derivative liabilities subject to netting arrangements, Net amount	42	70
Foreign exchange contracts
Derivative Asset
Derivatives subject to netting arrangements, Gross assets recognized	5,943	7,128
Total derivatives subject to netting arrangements, Gross amounts offset in the balance sheet	4,251	6,392
Derivatives subject to netting arrangements, Net assets recognized in the balance sheet	1,692	736
Total derivatives, Gross amounts not offset in the balance sheet, Financial instruments	66	146
Total derivatives, Gross amounts not offset in the balance sheet, Cash collateral received	0	0
Derivative assets subject to netting arrangements, Net amount	1,626	590
Derivative Liability
Derivatives subject to netting arrangements, Gross liabilities recognized	5,744	7,280
Derivatives subject to netting arrangements, Gross amounts offset in the balance sheet	4,685	5,484
Derivatives subject to netting arrangements, Net liabilities recognized in the balance sheet	1,059	1,796
Total derivatives, Gross amounts not offset in the balance sheet, Financial instruments	247	143
Total derivatives, Gross amounts not offset in the balance sheet, Cash collateral pledged	0	0
Derivative liabilities subject to netting arrangements, Net amount	812	1,653
Equity and other contracts
Derivative Asset
Derivatives subject to netting arrangements, Gross assets recognized	265	2
Total derivatives subject to netting arrangements, Gross amounts offset in the balance sheet	168	2
Derivatives subject to netting arrangements, Net assets recognized in the balance sheet	97	0
Total derivatives, Gross amounts not offset in the balance sheet, Financial instruments	28	0
Total derivatives, Gross amounts not offset in the balance sheet, Cash collateral received	0	0
Derivative assets subject to netting arrangements, Net amount	69	0
Derivative Liability
Derivatives subject to netting arrangements, Gross liabilities recognized	9	37
Derivatives subject to netting arrangements, Gross amounts offset in the balance sheet	0	13
Derivatives subject to netting arrangements, Net liabilities recognized in the balance sheet	9	24
Total derivatives, Gross amounts not offset in the balance sheet, Financial instruments	0	7
Total derivatives, Gross amounts not offset in the balance sheet, Cash collateral pledged	0	0
Derivative liabilities subject to netting arrangements, Net amount	$ 9	$ 17