Derivative instruments - Offsetting (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Derivative Asset
Derivatives subject to netting arrangements, Gross assets recognized	$ 13,102	$ 7,264
Total derivatives subject to netting arrangements, Gross amounts offset in the balance sheet	10,328	5,819
Derivatives subject to netting arrangements, Net assets recognized in the balance sheet	2,774	1,445
Total derivatives, Gross amounts not offset in the balance sheet, Financial instruments	501	251
Total derivatives, Gross amounts not offset in the balance sheet, Cash collateral received	0	0
Derivative assets subject to netting arrangements, Net amount	2,273	1,194
Total derivatives not subject to netting arrangements	3,109	1,797
Total derivatives, Gross assets recognized	16,211	9,061
Fair value after effect of master netting agreements	5,883	3,242
Total derivatives, Net amount	5,382	2,991
Reverse repurchase agreements, Gross assets recognized	97,971	112,355
Reverse repurchase agreements, Gross amounts offset in the balance sheet	80,203	93,794
Reverse repurchase agreements, Net assets recognized on the balance sheet	17,768	18,561
Reverse repurchase agreements, Gross amounts not offset in the balance sheet, Financial instruments	17,759	18,554
Reverse repurchase agreements, Gross amounts not offset in the balance sheet, Cash collateral received	0	0
Reverse repurchase agreements, Net amount	9	7
Securities borrowing, Gross assets recognized	9,613	11,621
Securities borrowing, Net assets recognized on the balance sheet	9,613	11,621
Securities borrowing, Gross amounts not offset in the balance sheet, Financial instruments	9,055	11,278
Securities borrowing, Net amount	558	343
Total, Gross assets recognized	123,795	133,037
Total, Gross amounts offset in the balance sheet	90,531	99,613
Total, Net assets recognized on the balance sheet	33,264	33,424
Total, Gross amounts not offset in the balance sheet, Financial instruments	27,315	30,083
Total, Gross amounts not offset in the balance sheet, Cash collateral received	0	0
Total, Net amount	5,949	3,341
Derivative Liability
Derivatives subject to netting arrangements, Gross liabilities recognized	16,913	8,428
Derivatives subject to netting arrangements, Gross amounts offset in the balance sheet	11,864	5,415
Derivatives subject to netting arrangements, Net liabilities recognized in the balance sheet	5,049	3,013
Total derivatives, Gross amounts not offset in the balance sheet, Financial instruments	1,997	1,615
Total derivatives, Gross amounts not offset in the balance sheet, Cash collateral pledged	0	0
Derivative liabilities subject to netting arrangements, Net amount	3,052	1,398
Total derivatives not subject to netting arrangements	1,241	778
Total derivatives, Gross liabilities recognized	18,154	9,206
Fair value after effect of master netting agreements	6,290	3,791
Total derivatives, Net amount	4,293	2,176
Repurchase agreements, Gross liabilities recognized	92,057	104,451
Repurchase agreements, Gross amounts offset in the balance sheet	80,203	93,794
Repurchase agreements, Net liabilities recognized on the balance sheet	11,854	10,657
Repurchase agreements, Gross amounts not offset in the balance sheet, Financial instruments	11,823	10,657
Repurchase agreements, Gross amounts not offset in the balance sheet, Cash collateral pledged	0	0
Repurchase agreements, Net amount	31	0
Securities lending, Gross liabilities recognized	750	718
Securities lending, Net liabilities recognized on the balance sheet	750	718
Securities lending, Gross amounts not offset in the balance sheet, Financial instruments	717	694
Securities lending, Net amount	33	24
Total, Gross liabilities recognized	110,961	114,375
Total, Gross amounts offset in the balance sheet	92,067	99,209
Total, Net liabilities recognized on the balance sheet	18,894	15,166
Total, Gross amounts not offset in the balance sheet, Financial instruments	14,537	12,966
Total, Gross amounts not offset in the balance sheet, Cash collateral pledged	0	0
Total, Net amount	4,357	2,200
Interest rate contracts
Derivative Asset
Derivatives subject to netting arrangements, Gross assets recognized	4,103	2,394
Total derivatives subject to netting arrangements, Gross amounts offset in the balance sheet	3,047	1,792
Derivatives subject to netting arrangements, Net assets recognized in the balance sheet	1,056	602
Total derivatives, Gross amounts not offset in the balance sheet, Financial instruments	369	207
Total derivatives, Gross amounts not offset in the balance sheet, Cash collateral received	0	0
Derivative assets subject to netting arrangements, Net amount	687	395
Derivative Liability
Derivatives subject to netting arrangements, Gross liabilities recognized	6,181	3,550
Derivatives subject to netting arrangements, Gross amounts offset in the balance sheet	3,479	1,986
Derivatives subject to netting arrangements, Net liabilities recognized in the balance sheet	2,702	1,564
Total derivatives, Gross amounts not offset in the balance sheet, Financial instruments	1,452	1,539
Total derivatives, Gross amounts not offset in the balance sheet, Cash collateral pledged	0	0
Derivative liabilities subject to netting arrangements, Net amount	1,250	25
Foreign exchange contracts
Derivative Asset
Derivatives subject to netting arrangements, Gross assets recognized	8,984	4,861
Total derivatives subject to netting arrangements, Gross amounts offset in the balance sheet	7,272	4,021
Derivatives subject to netting arrangements, Net assets recognized in the balance sheet	1,712	840
Total derivatives, Gross amounts not offset in the balance sheet, Financial instruments	132	44
Total derivatives, Gross amounts not offset in the balance sheet, Cash collateral received	0	0
Derivative assets subject to netting arrangements, Net amount	1,580	796
Derivative Liability
Derivatives subject to netting arrangements, Gross liabilities recognized	10,705	4,873
Derivatives subject to netting arrangements, Gross amounts offset in the balance sheet	8,382	3,428
Derivatives subject to netting arrangements, Net liabilities recognized in the balance sheet	2,323	1,445
Total derivatives, Gross amounts not offset in the balance sheet, Financial instruments	545	74
Total derivatives, Gross amounts not offset in the balance sheet, Cash collateral pledged	0	0
Derivative liabilities subject to netting arrangements, Net amount	1,778	1,371
Equity and other contracts
Derivative Asset
Derivatives subject to netting arrangements, Gross assets recognized	15	9
Total derivatives subject to netting arrangements, Gross amounts offset in the balance sheet	9	6
Derivatives subject to netting arrangements, Net assets recognized in the balance sheet	6	3
Total derivatives, Gross amounts not offset in the balance sheet, Financial instruments	0	0
Total derivatives, Gross amounts not offset in the balance sheet, Cash collateral received	0	0
Derivative assets subject to netting arrangements, Net amount	6	3
Derivative Liability
Derivatives subject to netting arrangements, Gross liabilities recognized	27	5
Derivatives subject to netting arrangements, Gross amounts offset in the balance sheet	3	1
Derivatives subject to netting arrangements, Net liabilities recognized in the balance sheet	24	4
Total derivatives, Gross amounts not offset in the balance sheet, Financial instruments	0	2
Total derivatives, Gross amounts not offset in the balance sheet, Cash collateral pledged	0	0
Derivative liabilities subject to netting arrangements, Net amount	$ 24	$ 2