Business Segments - Results of Operations and Average Assets by Segment (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Segment Reporting Information
Net interest income	$ 1,421	$ 1,438	$ 4,192	$ 4,411
Provision for credit losses	160	119	351	460
Net Interest Income After Provision for Credit Losses	1,261	1,319	3,841	3,951
Noninterest Income
Wealth and asset management revenue	163	145	483	434
Service charges on deposits	161	149	467	431
Commercial banking revenue	163	154	451	461
Card and processing revenue	106	104	316	310
Mortgage banking net revenue	50	57	154	184
Leasing business revenue	43	58	120	162
Other noninterest income	15	55	103	152
Securities gains (losses), net	10	(7)	23	3
Total noninterest income	711	715	2,117	2,137
Noninterest Expense
Compensation and benefits	690	629	2,099	2,036
Technology and communications	121	115	351	347
Net occupancy expense	81	84	251	248
Equipment expense	38	37	114	110
Marketing expense	26	35	92	96
Leasing business expense	21	29	69	94
Card and processing expense	22	21	63	63
Other noninterest expense	245	238	768	756
Total noninterest expense	1,244	1,188	3,807	3,750
Income (loss) before income taxes	728	846	2,151	2,338
Applicable income tax expense (benefit)	155	186	457	519
Net Income	573	660	1,694	1,819
Total goodwill	4,918	4,919	4,918	4,919	$ 4,919	$ 4,915
Total assets	214,318	212,967	214,318	212,967
Bank premises and equipment held for sale	24		24		19
Impairment losses on bank premises	0	0	0	2
Impairment losses and termination charges	0	1	0	2
Operating Segments | Commercial Banking
Segment Reporting Information
Net interest income	669	1,007	2,012	3,006
Provision for credit losses	76	0	284	37
Net Interest Income After Provision for Credit Losses	593	1,007	1,728	2,969
Noninterest Income
Wealth and asset management revenue	1	0	2	2
Service charges on deposits	104	95	307	275
Commercial banking revenue	162	154	446	459
Card and processing revenue	27	23	80	69
Mortgage banking net revenue	0	0	0	0
Leasing business revenue	43	58	120	162
Other noninterest income	11	24	46	68
Securities gains (losses), net	9	(1)	3	(9)
Total noninterest income	357	353	1,004	1,026
Noninterest Expense
Compensation and benefits	151	156	496	499
Technology and communications	3	4	10	10
Net occupancy expense	9	12	27	32
Equipment expense	7	7	21	22
Marketing expense	1	1	2	2
Leasing business expense	21	29	69	94
Card and processing expense	2	3	6	8
Other noninterest expense	276	266	797	849
Total noninterest expense	470	478	1,428	1,516
Income (loss) before income taxes	480	882	1,304	2,479
Applicable income tax expense (benefit)	87	164	224	470
Net Income	393	718	1,080	2,009
Total goodwill	2,324	2,324	2,324	2,324	2,324	2,324
Total assets	75,594	82,829	75,594	82,829
Operating Segments | Consumer and Small Business Banking
Segment Reporting Information
Net interest income	1,031	1,390	3,210	4,016
Provision for credit losses	78	105	232	221
Net Interest Income After Provision for Credit Losses	953	1,285	2,978	3,795
Noninterest Income
Wealth and asset management revenue	64	53	185	159
Service charges on deposits	56	55	159	159
Commercial banking revenue	1	1	4	3
Card and processing revenue	78	78	232	231
Mortgage banking net revenue	50	57	153	184
Leasing business revenue	0	0	0	0
Other noninterest income	31	30	86	83
Securities gains (losses), net	0	0	0	0
Total noninterest income	280	274	819	819
Noninterest Expense
Compensation and benefits	206	217	666	663
Technology and communications	7	7	22	20
Net occupancy expense	52	52	159	156
Equipment expense	13	11	38	32
Marketing expense	15	17	55	52
Leasing business expense	0	0	0	0
Card and processing expense	20	19	57	57
Other noninterest expense	291	301	871	920
Total noninterest expense	604	624	1,868	1,900
Income (loss) before income taxes	629	935	1,929	2,714
Applicable income tax expense (benefit)	132	196	405	569
Net Income	497	739	1,524	2,145
Total goodwill	2,369	2,369	2,369	2,369	2,369	2,365
Total assets	89,890	88,230	89,890	88,230
Impairment losses on bank premises				1
Operating Segments | Wealth and Asset Management
Segment Reporting Information
Net interest income	50	98	162	294
Provision for credit losses	0	1	0	1
Net Interest Income After Provision for Credit Losses	50	97	162	293
Noninterest Income
Wealth and asset management revenue	98	92	296	273
Service charges on deposits	0	0	1	0
Commercial banking revenue	0	0	1	1
Card and processing revenue	1	0	2	2
Mortgage banking net revenue	0	0	1	0
Leasing business revenue	0	0	0	0
Other noninterest income	0	2	1	2
Securities gains (losses), net	0	0	0	0
Total noninterest income	99	94	302	278
Noninterest Expense
Compensation and benefits	54	53	168	169
Technology and communications	0	0	1	1
Net occupancy expense	3	3	9	9
Equipment expense	0	0	0	0
Marketing expense	0	0	1	1
Leasing business expense	0	0	0	0
Card and processing expense	0	0	1	1
Other noninterest expense	38	34	112	105
Total noninterest expense	95	90	292	286
Income (loss) before income taxes	54	101	172	285
Applicable income tax expense (benefit)	12	22	36	59
Net Income	42	79	136	226
Total goodwill	225	226	225	226	226	226
Total assets	10,669	10,538	10,669	10,538
Operating Segments | Wealth and Asset Management | Revision of Prior Period, Adjustment
Noninterest Income
Wealth and asset management revenue					(186)	(177)	$ (180)
Noninterest Expense
Other noninterest expense					(186)	(177)	$ (180)
General Corporate and Other
Segment Reporting Information
Net interest income	(329)	(1,057)	(1,192)	(2,905)
Provision for credit losses	6	13	(165)	201
Net Interest Income After Provision for Credit Losses	(335)	(1,070)	(1,027)	(3,106)
Noninterest Income
Wealth and asset management revenue	0	0	0	0
Service charges on deposits	1	(1)	0	(3)
Commercial banking revenue	0	(1)	0	(2)
Card and processing revenue	0	3	2	8
Mortgage banking net revenue	0	0	0	0
Leasing business revenue	0	0	0	0
Other noninterest income	(27)	(1)	(30)	(1)
Securities gains (losses), net	1	(6)	20	12
Total noninterest income	(25)	(6)	(8)	14
Noninterest Expense
Compensation and benefits	279	203	769	705
Technology and communications	111	104	318	316
Net occupancy expense	17	17	56	51
Equipment expense	18	19	55	56
Marketing expense	10	17	34	41
Leasing business expense	0	0	0	0
Card and processing expense	0	(1)	(1)	(3)
Other noninterest expense	(360)	(363)	(1,012)	(1,118)
Total noninterest expense	75	(4)	219	48
Income (loss) before income taxes	(435)	(1,072)	(1,254)	(3,140)
Applicable income tax expense (benefit)	(76)	(196)	(208)	(579)
Net Income	(359)	(876)	(1,046)	(2,561)
Total goodwill	0	0	0	0	$ 0	$ 0
Total assets	38,165	31,370	38,165	31,370
Bank premises and equipment held for sale	$ 24	$ 22	$ 24	22
Impairment losses on bank premises				$ 1