Consolidated Statement of Cash Flows - USD ($) $ in Millions	3 Months Ended				9 Months Ended		12 Months Ended
	Sep. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Operating Activities:
Net income	$ 555	$ 634	$ 583	$ 508	$ 1,883	$ 1,678
Adjustments to reconcile net income to net cash provided by operating activities:
Deferred income tax expense (benefit)					(35)	15
Amortization of other intangible assets	59		59		175	178	$ 236
Other non-cash adjustments for depreciation, amortization and accretion, net					(793)	796
Losses (gains) related to investment securities, net					(2)	1
Change in trading account assets, net					74	21
Change in accrued interest and fees receivable, net					(60)	(55)
Change in collateral deposits, net					1,369	216
Change in unrealized losses (gains) on foreign exchange derivatives, net					(2,934)	254
Change in other assets, net					(430)	(279)
Change in accrued expenses and other liabilities, net					526	1,471
Other, net					383	341
Net cash provided by operating activities					156	4,637
Investing Activities:
Net decrease (increase) in interest-bearing deposits with banks					(7,002)	10,716
Net decrease (increase) in securities purchased under resale agreements					(3,012)	1,638
Proceeds from sales of available-for-sale securities					2,245	5,185
Proceeds from maturities of available-for-sale securities					16,257	15,387
Purchases of available-for-sale securities					(30,344)	(30,204)
Purchases of held-to-maturity securities under the MMLF program					(29,242)	0
Proceeds from maturities of held-to-maturity securities under the MMLF program					24,457	0
Proceeds from maturities of held-to-maturity securities					10,863	7,199
Purchases of held-to-maturity securities					(8,994)	(5,036)
Net (increase) in loans					(725)	(1,220)
Business acquisitions, net of cash acquired					0	(54)
Purchases of equity investments and other long-term assets					(1,237)	(611)
Purchases of premises and equipment, net					(424)	(569)
Other, net					1,036	466
Net cash (used in) provided by investing activities					(26,122)	2,897
Financing Activities:
Net (decrease) increase in time deposits					(35,146)	(11,341)
Net increase in all other deposits					50,786	1,868
Net increase in short-term borrowings under money market liquidity facility					4,819	0
Net increase in other short-term borrowings					6,327	4,229
Proceeds from issuance of long-term debt, net of issuance costs					2,497	0
Payments for long-term debt and obligations under finance leases					(24)	(47)
Payments for redemption of preferred stock					(500)	0
Repurchases of common stock					(515)	(1,100)
Repurchases of common stock for employee tax withholding					(66)	(66)
Payments for cash dividends					(666)	(691)
Net cash provided by (used in) financing activities					27,512	(7,148)
Net increase					1,546	386
Cash and due from banks at beginning of period		$ 3,302		$ 3,212	3,302	3,212	3,212
Cash and due from banks at end of period	$ 4,848		$ 3,598		$ 4,848	$ 3,598	$ 3,302