Business Segments - Results of Operations and Average Assets by Segment (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Segment Reporting Information
Net interest income	$ 1,387	$ 1,457	$ 2,771	$ 2,974
Provision for (benefit from) credit losses	97	177	191	341
Net Interest Income After Provision for Credit Losses	1,290	1,280	2,580	2,633
Noninterest Income
Wealth and asset management revenue	159	143	320	289
Service charges on deposits	156	144	306	281
Commercial banking revenue	144	146	288	307
Card and processing revenue	108	106	210	206
Mortgage banking net revenue	50	59	104	127
Leasing business revenue	38	47	77	104
Other noninterest income	37	74	88	97
Securities gains (losses), net	3	7	13	11
Total noninterest income	695	726	1,406	1,422
Noninterest Expense
Compensation and benefits	656	650	1,409	1,407
Technology and communications	114	114	231	232
Net occupancy expense	83	83	170	164
Equipment expense	38	36	76	73
Leasing business expense	34	31	66	60
Marketing expense	22	31	48	65
Card and processing expense	21	20	41	42
Other noninterest expense	253	266	521	519
Total noninterest expense	1,221	1,231	2,562	2,562
Income (loss) before income taxes	764	775	1,424	1,493
Applicable income tax expense (benefit)	163	174	302	334
Net Income	601	601	1,122	1,159
Total goodwill	4,918	4,919	4,918	4,919	$ 4,919
Total assets	213,262	207,276	213,262	207,276
Bank premises and equipment held for sale	16		16		19
Impairment losses on bank premises	0	0	0	1
Impairment losses and termination charges	0	0	0	1
Operating Segments | Commercial Banking
Segment Reporting Information
Net interest income	656	1,021	1,342	1,997
Provision for (benefit from) credit losses	137	(9)	208	37
Net Interest Income After Provision for Credit Losses	519	1,030	1,134	1,960
Noninterest Income
Wealth and asset management revenue	1	0	2	1
Service charges on deposits	104	92	203	180
Commercial banking revenue	142	147	285	305
Card and processing revenue	28	23	53	45
Mortgage banking net revenue	0	0	0	0
Leasing business revenue	38	47	77	104
Other noninterest income	17	28	34	44
Securities gains (losses), net	(7)	(1)	(6)	(8)
Total noninterest income	323	336	648	671
Noninterest Expense
Compensation and benefits	156	153	345	343
Technology and communications	3	3	8	5
Net occupancy expense	9	10	18	20
Equipment expense	7	7	14	14
Leasing business expense	1	1	1	1
Marketing expense	22	31	48	65
Card and processing expense	2	2	4	5
Other noninterest expense	257	279	520	583
Total noninterest expense	457	486	958	1,036
Income (loss) before income taxes	385	880	824	1,595
Applicable income tax expense (benefit)	65	169	136	305
Net Income	320	711	688	1,290
Total goodwill	2,324	2,324	2,324	2,324
Total assets	77,123	83,238	77,123	83,238
Operating Segments | Consumer and Small Business Banking
Segment Reporting Information
Net interest income	1,055	1,370	2,180	2,628
Provision for (benefit from) credit losses	70	65	154	116
Net Interest Income After Provision for Credit Losses	985	1,305	2,026	2,512
Noninterest Income
Wealth and asset management revenue	62	52	121	106
Service charges on deposits	52	53	103	103
Commercial banking revenue	1	1	3	2
Card and processing revenue	79	79	154	155
Mortgage banking net revenue	50	59	104	127
Leasing business revenue	0	0	0	0
Other noninterest income	28	27	55	52
Securities gains (losses), net	0	0	0	0
Total noninterest income	272	271	540	545
Noninterest Expense
Compensation and benefits	226	222	460	446
Technology and communications	8	6	14	13
Net occupancy expense	53	52	107	104
Equipment expense	13	10	26	21
Leasing business expense	19	18	42	35
Marketing expense	0	0	0	0
Card and processing expense	19	19	37	38
Other noninterest expense	288	305	581	619
Total noninterest expense	626	632	1,267	1,276
Income (loss) before income taxes	631	944	1,299	1,781
Applicable income tax expense (benefit)	132	198	273	373
Net Income	499	746	1,026	1,408
Total goodwill	2,369	2,369	2,369	2,369
Total assets	90,242	85,755	90,242	85,755
Impairment losses on bank premises				1
Operating Segments | Wealth and Asset Management
Segment Reporting Information
Net interest income	54	95	112	196
Provision for (benefit from) credit losses	0	0	0	0
Net Interest Income After Provision for Credit Losses	54	95	112	196
Noninterest Income
Wealth and asset management revenue	96	89	197	182
Service charges on deposits	0	0	0	0
Commercial banking revenue	1	0	1	0
Card and processing revenue	1	1	1	1
Mortgage banking net revenue	0	0	0	0
Leasing business revenue	0	0	0	0
Other noninterest income	0	1	1	0
Securities gains (losses), net	0	0	0	0
Total noninterest income	98	91	200	183
Noninterest Expense
Compensation and benefits	52	55	114	116
Technology and communications	0	0	0	0
Net occupancy expense	3	3	6	6
Equipment expense	0	0	0	0
Leasing business expense	0	0	0	1
Marketing expense	0	0	0	0
Card and processing expense	0	0	1	0
Other noninterest expense	38	35	74	71
Total noninterest expense	93	93	195	194
Income (loss) before income taxes	59	93	117	185
Applicable income tax expense (benefit)	12	20	25	39
Net Income	47	73	92	146
Total goodwill	225	226	225	226
Total assets	10,480	10,691	10,480	10,691
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	(378)	(1,029)	(863)	(1,847)
Provision for (benefit from) credit losses	(110)	121	(171)	188
Net Interest Income After Provision for Credit Losses	(268)	(1,150)	(692)	(2,035)
Noninterest Income
Wealth and asset management revenue	0	2	0	0
Service charges on deposits	0	(1)	0	(2)
Commercial banking revenue	0	(2)	(1)	0
Card and processing revenue	0	3	2	5
Mortgage banking net revenue	0	0	0	0
Leasing business revenue	0	0	0	0
Other noninterest income	(8)	18	(2)	1
Securities gains (losses), net	10	8	19	19
Total noninterest income	2	28	18	23
Noninterest Expense
Compensation and benefits	222	220	490	502
Technology and communications	103	105	209	214
Net occupancy expense	18	18	39	34
Equipment expense	18	19	36	38
Leasing business expense	14	12	23	23
Marketing expense	0	0	0	0
Card and processing expense	0	(1)	(1)	(1)
Other noninterest expense	(330)	(353)	(654)	(754)
Total noninterest expense	45	20	142	56
Income (loss) before income taxes	(311)	(1,142)	(816)	(2,068)
Applicable income tax expense (benefit)	(46)	(213)	(132)	(383)
Net Income	(265)	(929)	(684)	(1,685)
Total goodwill	0	0	0	0
Total assets	35,417	27,592	35,417	27,592
Bank premises and equipment held for sale	$ 16	$ 22	$ 16	$ 22