Derivative instruments - Offsetting (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Derivative Asset
Derivatives subject to netting arrangements, Gross assets recognized	$ 7,584	$ 7,264
Total derivatives subject to netting arrangements, Gross amounts offset in the balance sheet	5,640	5,819
Derivatives subject to netting arrangements, Net assets recognized in the balance sheet	1,944	1,445
Total derivatives, Gross amounts not offset in the balance sheet, Financial instruments	392	251
Total derivatives, Gross amounts not offset in the balance sheet, Cash collateral received	0	0
Derivative assets subject to netting arrangements, Net amount	1,552	1,194
Total derivatives not subject to netting arrangements	2,389	1,797
Total derivatives, Gross assets recognized	9,973	9,061
Fair value after effect of master netting agreements	4,333	3,242
Total derivatives, Net amount	3,941	2,991
Reverse repurchase agreements, Gross assets recognized	72,781	112,355
Reverse repurchase agreements, Gross amounts offset in the balance sheet	48,615	93,794
Reverse repurchase agreements, Net assets recognized on the balance sheet	24,166	18,561
Reverse repurchase agreements, Gross amounts not offset in the balance sheet, Financial instruments	24,140	18,554
Reverse repurchase agreements, Gross amounts not offset in the balance sheet, Cash collateral received	0	0
Reverse repurchase agreements, Net amount	26	7
Securities borrowing, Gross assets recognized	12,472	11,621
Securities borrowing, Net assets recognized on the balance sheet	12,472	11,621
Securities borrowing, Gross amounts not offset in the balance sheet, Financial instruments	11,843	11,278
Securities borrowing, Net amount	629	343
Total, Gross assets recognized	95,226	133,037
Total, Gross amounts offset in the balance sheet	54,255	99,613
Total, Net assets recognized on the balance sheet	40,971	33,424
Total, Gross amounts not offset in the balance sheet, Financial instruments	36,375	30,083
Total, Gross amounts not offset in the balance sheet, Cash collateral received	0	0
Total, Net amount	4,596	3,341
Derivative Liability
Derivatives subject to netting arrangements, Gross liabilities recognized	9,275	8,428
Derivatives subject to netting arrangements, Gross amounts offset in the balance sheet	5,817	5,415
Derivatives subject to netting arrangements, Net liabilities recognized in the balance sheet	3,458	3,013
Total derivatives, Gross amounts not offset in the balance sheet, Financial instruments	2,999	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	459	1,398
Total derivatives not subject to netting arrangements	417	778
Total derivatives, Gross liabilities recognized	9,692	9,206
Fair value after effect of master netting agreements	3,875	3,791
Total derivatives, Net amount	876	2,176
Repurchase agreements, Gross liabilities recognized	59,794	104,451
Repurchase agreements, Gross amounts offset in the balance sheet	48,615	93,794
Repurchase agreements, Net liabilities recognized on the balance sheet	11,179	10,657
Repurchase agreements, Gross amounts not offset in the balance sheet, Financial instruments	11,175	10,657
Repurchase agreements, Gross amounts not offset in the balance sheet, Cash collateral pledged	0	0
Repurchase agreements, Net amount	4	0
Securities lending, Gross liabilities recognized	982	718
Securities lending, Net liabilities recognized on the balance sheet	982	718
Securities lending, Gross amounts not offset in the balance sheet, Financial instruments	962	694
Securities lending, Net amount	20	24
Total, Gross liabilities recognized	70,468	114,375
Total, Gross amounts offset in the balance sheet	54,432	99,209
Total, Net liabilities recognized on the balance sheet	16,036	15,166
Total, Gross amounts not offset in the balance sheet, Financial instruments	15,136	12,966
Total, Gross amounts not offset in the balance sheet, Cash collateral pledged	0	0
Total, Net amount	900	2,200
Interest rate contracts
Derivative Asset
Derivatives subject to netting arrangements, Gross assets recognized	3,549	2,394
Total derivatives subject to netting arrangements, Gross amounts offset in the balance sheet	2,436	1,792
Derivatives subject to netting arrangements, Net assets recognized in the balance sheet	1,113	602
Total derivatives, Gross amounts not offset in the balance sheet, Financial instruments	384	207
Total derivatives, Gross amounts not offset in the balance sheet, Cash collateral received	0	0
Derivative assets subject to netting arrangements, Net amount	729	395
Derivative Liability
Derivatives subject to netting arrangements, Gross liabilities recognized	5,563	3,550
Derivatives subject to netting arrangements, Gross amounts offset in the balance sheet	2,680	1,986
Derivatives subject to netting arrangements, Net liabilities recognized in the balance sheet	2,883	1,564
Total derivatives, Gross amounts not offset in the balance sheet, Financial instruments	2,849	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	34	25
Foreign exchange contracts
Derivative Asset
Derivatives subject to netting arrangements, Gross assets recognized	4,026	4,861
Total derivatives subject to netting arrangements, Gross amounts offset in the balance sheet	3,204	4,021
Derivatives subject to netting arrangements, Net assets recognized in the balance sheet	822	840
Total derivatives, Gross amounts not offset in the balance sheet, Financial instruments	7	44
Total derivatives, Gross amounts not offset in the balance sheet, Cash collateral received	0	0
Derivative assets subject to netting arrangements, Net amount	815	796
Derivative Liability
Derivatives subject to netting arrangements, Gross liabilities recognized	3,690	4,873
Derivatives subject to netting arrangements, Gross amounts offset in the balance sheet	3,134	3,428
Derivatives subject to netting arrangements, Net liabilities recognized in the balance sheet	556	1,445
Total derivatives, Gross amounts not offset in the balance sheet, Financial instruments	150	74
Total derivatives, Gross amounts not offset in the balance sheet, Cash collateral pledged	0	0
Derivative liabilities subject to netting arrangements, Net amount	406	1,371
Equity and other contracts
Derivative Asset
Derivatives subject to netting arrangements, Gross assets recognized	9	9
Total derivatives subject to netting arrangements, Gross amounts offset in the balance sheet	0	6
Derivatives subject to netting arrangements, Net assets recognized in the balance sheet	9	3
Total derivatives, Gross amounts not offset in the balance sheet, Financial instruments	1	0
Total derivatives, Gross amounts not offset in the balance sheet, Cash collateral received	0	0
Derivative assets subject to netting arrangements, Net amount	8	3
Derivative Liability
Derivatives subject to netting arrangements, Gross liabilities recognized	22	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	19	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	$ 19	$ 2