Fair value measurement - Financial Instruments (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Assets:
Securities held-to-maturity	$ 45,983	$ 34,805
Liabilities:
Long-term debt	399	387
Estimated fair value
Assets:
Interest-bearing deposits with the Federal Reserve and other central banks	112,728	95,042
Interest-bearing deposits with banks	18,063	14,832
Federal funds sold and securities purchased under resale agreements	36,638	30,182
Securities held-to-maturity	45,983	34,805
Loans	54,377	54,194
Other financial assets	5,941	6,063
Total assets	273,730	235,118
Liabilities:
Noninterest-bearing deposits	78,100	57,630
Interest-bearing deposits	226,917	200,846
Federal funds purchased and securities sold under repurchase agreements	14,512	11,401
Payables to customers and broker-dealers	25,012	18,758
Commercial paper	665	3,959
Borrowings	1,852	917
Long-term debt	28,875	27,858
Total liabilities	375,933	321,369
Estimated fair value | Level 1
Assets:
Interest-bearing deposits with the Federal Reserve and other central banks	0	0
Interest-bearing deposits with banks	0	0
Federal funds sold and securities purchased under resale agreements	0	0
Securities held-to-maturity	5,815	4,630
Loans	0	0
Other financial assets	4,776	4,830
Total assets	10,591	9,460
Liabilities:
Noninterest-bearing deposits	0	0
Interest-bearing deposits	0	0
Federal funds purchased and securities sold under repurchase agreements	0	0
Payables to customers and broker-dealers	0	0
Commercial paper	0	0
Borrowings	0	0
Long-term debt	0	0
Total liabilities	0	0
Estimated fair value | Level 2
Assets:
Interest-bearing deposits with the Federal Reserve and other central banks	112,728	95,042
Interest-bearing deposits with banks	18,063	14,832
Federal funds sold and securities purchased under resale agreements	36,638	30,182
Securities held-to-maturity	40,168	30,175
Loans	54,377	54,194
Other financial assets	1,165	1,233
Total assets	263,139	225,658
Liabilities:
Noninterest-bearing deposits	78,100	57,630
Interest-bearing deposits	226,917	200,846
Federal funds purchased and securities sold under repurchase agreements	14,512	11,401
Payables to customers and broker-dealers	25,012	18,758
Commercial paper	665	3,959
Borrowings	1,852	917
Long-term debt	28,875	27,858
Total liabilities	375,933	321,369
Estimated fair value | Level 3
Assets:
Interest-bearing deposits with the Federal Reserve and other central banks	0	0
Interest-bearing deposits with banks	0	0
Federal funds sold and securities purchased under resale agreements	0	0
Securities held-to-maturity	0	0
Loans	0	0
Other financial assets	0	0
Total assets	0	0
Liabilities:
Noninterest-bearing deposits	0	0
Interest-bearing deposits	0	0
Federal funds purchased and securities sold under repurchase agreements	0	0
Payables to customers and broker-dealers	0	0
Commercial paper	0	0
Borrowings	0	0
Long-term debt	0	0
Total liabilities	0	0
Carrying amount
Assets:
Interest-bearing deposits with the Federal Reserve and other central banks	112,728	95,042
Interest-bearing deposits with banks	18,045	14,811
Federal funds sold and securities purchased under resale agreements	36,638	30,182
Securities held-to-maturity	44,615	34,483
Loans	54,067	53,718
Other financial assets	5,941	6,063
Total assets	272,034	234,299
Liabilities:
Noninterest-bearing deposits	78,100	57,630
Interest-bearing deposits	227,370	201,836
Federal funds purchased and securities sold under repurchase agreements	14,512	11,401
Payables to customers and broker-dealers	25,012	18,758
Commercial paper	665	3,959
Borrowings	1,852	917
Long-term debt	27,167	27,114
Total liabilities	$ 374,678	$ 321,615