Fair value measurement - Financial Instruments (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Assets:
Securities held-to-maturity	$ 38,418	$ 34,805
Liabilities:
Long-term debt	397	387
Estimated fair value
Assets:
Interest-bearing deposits with the Federal Reserve and other central banks	146,535	95,042
Interest-bearing deposits with banks	22,689	14,832
Federal funds sold and securities purchased under resale agreements	27,363	30,182
Securities held-to-maturity	38,418	34,805
Loans	61,482	54,194
Other financial assets	6,289	6,063
Total assets	302,776	235,118
Liabilities:
Noninterest-bearing deposits	96,600	57,630
Interest-bearing deposits	239,459	200,846
Federal funds purchased and securities sold under repurchase agreements	13,128	11,401
Payables to customers and broker-dealers	24,016	18,758
Commercial paper	1,121	3,959
Borrowings	1,767	917
Long-term debt	27,521	27,858
Total liabilities	403,612	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	4,014	4,630
Loans	0	0
Other financial assets	5,091	4,830
Total assets	9,105	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	146,535	95,042
Interest-bearing deposits with banks	22,689	14,832
Federal funds sold and securities purchased under resale agreements	27,363	30,182
Securities held-to-maturity	34,404	30,175
Loans	61,482	54,194
Other financial assets	1,198	1,233
Total assets	293,671	225,658
Liabilities:
Noninterest-bearing deposits	96,600	57,630
Interest-bearing deposits	239,459	200,846
Federal funds purchased and securities sold under repurchase agreements	13,128	11,401
Payables to customers and broker-dealers	24,016	18,758
Commercial paper	1,121	3,959
Borrowings	1,767	917
Long-term debt	27,521	27,858
Total liabilities	403,612	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	146,535	95,042
Interest-bearing deposits with banks	22,672	14,811
Federal funds sold and securities purchased under resale agreements	27,363	30,182
Securities held-to-maturity	37,305	34,483
Loans	61,174	53,718
Other financial assets	6,289	6,063
Total assets	301,338	234,299
Liabilities:
Noninterest-bearing deposits	96,600	57,630
Interest-bearing deposits	240,117	201,836
Federal funds purchased and securities sold under repurchase agreements	13,128	11,401
Payables to customers and broker-dealers	24,016	18,758
Commercial paper	1,121	3,959
Borrowings	1,767	917
Long-term debt	27,097	27,114
Total liabilities	$ 403,846	$ 321,615