Loans and Allowance for Credit Losses - Activity in Allowance for Credit Losses (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	$ 7,934	$ 7,695	$ 7,839	$ 7,404
Allowance for acquired credit losses				127
Provision for credit losses	557	515	1,678	1,763
Loans charged-off	669	508	1,916	1,732
Less recoveries of loans charged-off	(105)	(88)	(326)	(290)
Net loan charge-offs (recoveries)	564	420	1,590	1,442
Balance at end of period	7,927	7,790	7,927	7,790
Add
Allowance for acquired credit losses				127
Provision for credit losses	557	515	1,678	1,763
Deduct
Loans charged-off	669	508	1,916	1,732
Less recoveries of loans charged-off	(105)	(88)	(326)	(290)
Net loan charge-offs (recoveries)	564	420	1,590	1,442
Change in accounting principle
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period				(62)
Commercial | Commercial
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	2,180	2,209	2,119	2,163
Allowance for acquired credit losses				0
Provision for credit losses	155	(14)	475	169
Loans charged-off	165	110	484	283
Less recoveries of loans charged-off	(18)	(18)	(78)	(54)
Net loan charge-offs (recoveries)	147	92	406	229
Balance at end of period	2,188	2,103	2,188	2,103
Add
Allowance for acquired credit losses				0
Provision for credit losses	155	(14)	475	169
Deduct
Loans charged-off	165	110	484	283
Less recoveries of loans charged-off	(18)	(18)	(78)	(54)
Net loan charge-offs (recoveries)	147	92	406	229
Commercial | Commercial | Change in accounting principle
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period				0
Commercial | Commercial real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	1,596	1,473	1,620	1,325
Allowance for acquired credit losses				127
Provision for credit losses	49	266	82	430
Loans charged-off	80	51	152	205
Less recoveries of loans charged-off	(10)	(2)	(25)	(13)
Net loan charge-offs (recoveries)	70	49	127	192
Balance at end of period	1,575	1,690	1,575	1,690
Add
Allowance for acquired credit losses				127
Provision for credit losses	49	266	82	430
Deduct
Loans charged-off	80	51	152	205
Less recoveries of loans charged-off	(10)	(2)	(25)	(13)
Net loan charge-offs (recoveries)	70	49	127	192
Commercial | Commercial real estate | Change in accounting principle
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period				0
Consumer | Residential mortgages
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	836	899	827	926
Allowance for acquired credit losses				0
Provision for credit losses	(36)	(49)	(31)	68
Loans charged-off	3	1	10	126
Less recoveries of loans charged-off	(6)	(4)	(17)	(16)
Net loan charge-offs (recoveries)	(3)	(3)	(7)	110
Balance at end of period	803	853	803	853
Add
Allowance for acquired credit losses				0
Provision for credit losses	(36)	(49)	(31)	68
Deduct
Loans charged-off	3	1	10	126
Less recoveries of loans charged-off	(6)	(4)	(17)	(16)
Net loan charge-offs (recoveries)	(3)	(3)	(7)	110
Consumer | Residential mortgages | Change in accounting principle
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period				(31)
Consumer | Credit card
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	2,498	2,185	2,403	2,020
Allowance for acquired credit losses				0
Provision for credit losses	349	285	1,055	851
Loans charged-off	347	259	1,042	716
Less recoveries of loans charged-off	(48)	(39)	(132)	(122)
Net loan charge-offs (recoveries)	299	220	910	594
Balance at end of period	2,548	2,250	2,548	2,250
Add
Allowance for acquired credit losses				0
Provision for credit losses	349	285	1,055	851
Deduct
Loans charged-off	347	259	1,042	716
Less recoveries of loans charged-off	(48)	(39)	(132)	(122)
Net loan charge-offs (recoveries)	299	220	910	594
Consumer | Credit card | Change in accounting principle
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period				(27)
Consumer | Other retail
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	824	929	870	970
Allowance for acquired credit losses				0
Provision for credit losses	40	27	97	245
Loans charged-off	74	87	228	402
Less recoveries of loans charged-off	(23)	(25)	(74)	(85)
Net loan charge-offs (recoveries)	51	62	154	317
Balance at end of period	813	894	813	894
Add
Allowance for acquired credit losses				0
Provision for credit losses	40	27	97	245
Deduct
Loans charged-off	74	87	228	402
Less recoveries of loans charged-off	(23)	(25)	(74)	(85)
Net loan charge-offs (recoveries)	$ 51	$ 62	$ 154	317
Consumer | Other retail | Change in accounting principle
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period				$ (4)