Loans - Summary of Credit Concentration by Region (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Product Information [Line Items]
Loans and Leases Receivable, Gross	$ 131,321	$ 110,345
Concentration Risk,Percentage	100.00%	100.00%
Americas [Member]
Product Information [Line Items]
Concentration Risk,Percentage	75.00%	73.00%
Europe, Middle East and Africa [Member]
Product Information [Line Items]
Concentration Risk,Percentage	19.00%	21.00%
Asia [Member]
Product Information [Line Items]
Concentration Risk,Percentage	6.00%	6.00%
Corporate [Member]
Product Information [Line Items]
Loans and Leases Receivable, Gross	$ 68,530	$ 46,307
Concentration Risk,Percentage	100.00%	100.00%
Corporate [Member] | Americas [Member]
Product Information [Line Items]
Concentration Risk,Percentage	67.00%	60.00%
Corporate [Member] | Europe, Middle East and Africa [Member]
Product Information [Line Items]
Concentration Risk,Percentage	26.00%	31.00%
Corporate [Member] | Asia [Member]
Product Information [Line Items]
Concentration Risk,Percentage	7.00%	9.00%
Wealth management [Member]
Product Information [Line Items]
Loans and Leases Receivable, Gross	$ 29,017	$ 27,940
Concentration Risk,Percentage	100.00%	100.00%
Wealth management [Member] | Americas [Member]
Product Information [Line Items]
Concentration Risk,Percentage	88.00%	88.00%
Wealth management [Member] | Europe, Middle East and Africa [Member]
Product Information [Line Items]
Concentration Risk,Percentage	9.00%	9.00%
Wealth management [Member] | Asia [Member]
Product Information [Line Items]
Concentration Risk,Percentage	3.00%	3.00%
Commercial real estate [Member]
Product Information [Line Items]
Loans and Leases Receivable, Gross	$ 16,830	$ 17,743
Concentration Risk,Percentage	100.00%	100.00%
Commercial real estate [Member] | Americas [Member]
Product Information [Line Items]
Concentration Risk,Percentage	69.00%	69.00%
Commercial real estate [Member] | Europe, Middle East and Africa [Member]
Product Information [Line Items]
Concentration Risk,Percentage	21.00%	21.00%
Commercial real estate [Member] | Asia [Member]
Product Information [Line Items]
Concentration Risk,Percentage	10.00%	10.00%
Residential real estate [Member]
Product Information [Line Items]
Loans and Leases Receivable, Gross	$ 4,413	$ 6,958
Concentration Risk,Percentage	100.00%	100.00%
Residential real estate [Member] | Americas [Member]
Product Information [Line Items]
Concentration Risk,Percentage	87.00%	90.00%
Residential real estate [Member] | Europe, Middle East and Africa [Member]
Product Information [Line Items]
Concentration Risk,Percentage	11.00%	9.00%
Residential real estate [Member] | Asia [Member]
Product Information [Line Items]
Concentration Risk,Percentage	2.00%	1.00%
Installment [Member]
Product Information [Line Items]
Loans and Leases Receivable, Gross	$ 4,826	$ 4,747
Concentration Risk,Percentage	100.00%	100.00%
Installment [Member] | Americas [Member]
Product Information [Line Items]
Concentration Risk,Percentage	100.00%	100.00%
Credit cards [Member]
Product Information [Line Items]
Loans and Leases Receivable, Gross	$ 2,081	$ 1,858
Concentration Risk,Percentage	100.00%	100.00%
Credit cards [Member] | Americas [Member]
Product Information [Line Items]
Concentration Risk,Percentage	100.00%	100.00%
Other [Member]
Product Information [Line Items]
Loans and Leases Receivable, Gross	$ 5,624	$ 4,792
Concentration Risk,Percentage	100.00%	100.00%
Other [Member] | Americas [Member]
Product Information [Line Items]
Concentration Risk,Percentage	87.00%	87.00%
Other [Member] | Europe, Middle East and Africa [Member]
Product Information [Line Items]
Concentration Risk,Percentage	12.00%	12.00%
Other [Member] | Asia [Member]
Product Information [Line Items]
Concentration Risk,Percentage	1.00%	1.00%