Consolidated Statement of Cash Flows - USD ($) $ in Millions	1 Months Ended	3 Months Ended				9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Operating Activities:
Net income		$ 714	$ 519	$ 555	$ 634	$ 1,996	$ 1,883
Adjustments to reconcile net income to net cash provided by operating activities:
Deferred income tax (benefit)						(52)	(35)
Amortization of other intangible assets		62		59		183	175	$ 234
Other non-cash adjustments for depreciation, amortization and accretion, net						1,015	(793)
Losses (gains) related to investment securities, net						1	(2)
Provision for credit losses						(26)	88
Change in trading account assets, net						94	74
Change in accrued interest and fees receivable, net						(302)	(60)
Change in collateral deposits, net						(7,723)	1,369
Change in unrealized losses (gains) on foreign exchange derivatives, net						(8,131)	(2,934)
Change in other assets, net						279	(430)
Change in accrued expenses and other liabilities, net						1,468	526
Other, net						261	295
Net cash (used in) provided by operating activities						(10,937)	156
Investing Activities:
Net (increase) decrease in interest-bearing deposits with banks						9,407	(7,002)
Net (increase) decrease in securities purchased under resale agreements						259	(3,012)
Proceeds from sales of available-for-sale securities						9,252	2,245
Proceeds from maturities of available-for-sale securities						16,281	16,257
Purchases of available-for-sale securities						(39,972)	(30,344)
Purchases of held-to-maturity securities under the MMLF program						0	(29,242)
Proceeds from maturities of held-to-maturity securities under the MMLF program						3,299	24,457
Proceeds from maturities of held-to-maturity securities						12,564	10,863
Purchases of held-to-maturity securities						(5,984)	(8,994)
Sale of loans						64	242
Net (increase) in loans						(4,873)	(967)
Business acquisitions, net of cash acquired						(346)	0
Divestitures						13	0
Purchases of equity investments and other long-term assets						(122)	(1,237)
Purchases of premises and equipment, net						(556)	(424)
Other, net						236	1,036
Net cash provided by (used in) investing activities						(478)	(26,122)
Financing Activities:
Net (decrease) increase in time deposits						(1,643)	(35,146)
Net increase (decrease) in all other deposits						21,227	50,786
Net (decrease) increase in securities sold under repurchase agreements						(2,776)	1,328
Net (decrease) increase in short-term borrowings under money market liquidity facility						(3,302)	4,819
Net (decrease) increase in other short-term borrowings						(137)	4,999
Proceeds from issuance of long-term debt, net of issuance costs						844	2,497
Payments for long-term debt and obligations under finance leases						(1,530)	(24)
Payments for redemption of preferred stock						(500)	(500)
Proceeds from issuance of common stock, net of issuance costs	$ 1,900					1,900	0
Repurchases of common stock						(900)	(515)
Repurchases of common stock for employee tax withholding						(6)	(66)
Payments for cash dividends						(623)	(666)
Net cash (used in) provided by financing activities						12,554	27,512
Net increase						1,139	1,546
Cash and due from banks at beginning of period			$ 3,467		$ 3,302	3,467	3,302	3,302
Cash and due from banks at end of period	$ 4,606	$ 4,606		$ 4,848		$ 4,606	$ 4,848	$ 3,467