Loans Held-for-Investment and Allowance for Loan Losses - Schedule of Company's Internal Ratings of its Loans Held-for-Investment, Including The Year of Origination, by Portfolio Segments (Detail) - USD ($) $ in Millions	Jun. 30, 2024	Dec. 31, 2023	Jun. 30, 2023
Financing Receivable, Credit Quality Indicator [Line Items]
2024	$ 1,669	$ 2,531	$ 1,252
2023	1,768	2,036	2,605
2022	1,770	1,062	1,217
2021	968	518	587
2020	435	240	274
Prior	743	613	694
Revolving Loans Amortized Cost Basis	167	149	149
Total	7,520	7,149	6,778
Charge-Off [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2023		1
2022	1	1	1
Prior	1
Total	2	2	1
C&I [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2024	373	733	344
2023	434	279	476
2022	203	75	109
2021	67	37	46
2020	30	16	19
Prior	35	25	28
Total	1,142	1,165	1,022
C&I [Member] | Charge-Off [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2022		1	1
Prior	1
Total	1	1	1
Municipal [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2024	148	25	11
2023	31	83	84
2022	80	16	18
2021	15	10	14
2020	9	1	2
Prior	76	80	87
Total	359	215	216
Agriculture [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2024	41	64	30
2023	36	15	44
2022	5	4	5
2021	3	1	2
2020	1	1	1
Total	86	85	82
Construction & Development [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2024	317	532	254
2023	355	317	510
2022	218	79	104
2021	66	20	24
2020	17	9	11
Prior	13	6	12
Total	986	963	915
Farm [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2024	63	101	63
2023	52	111	127
2022	82	73	79
2021	68	29	31
2020	27	8	9
Prior	27	23	27
Total	319	345	336
Non-Owner Occupied CRE [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2024	119	169	101
2023	89	238	240
2022	242	175	190
2021	169	113	126
2020	77	54	59
Prior	120	79	95
Total	816	828	811
Owner Occupied CRE [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2024	65	158	69
2023	151	312	326
2022	325	225	241
2021	212	114	122
2020	107	70	80
Prior	190	158	174
Total	1,050	1,037	1,012
Residential [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2024	287	482	229
2023	414	421	469
2022	413	318	342
2021	296	163	177
2020	147	70	75
Prior	275	239	266
Revolving Loans Amortized Cost Basis	159	142	141
Total	1,991	1,835	1,699
Auto [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2024	215	195	110
2023	155	213	266
2022	167	75	100
2021	55	27	39
2020	17	10	16
Prior	6	2	4
Total	615	522	535
Auto [Member] | Charge-Off [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2022	1	1
Total	1	1
Non-Auto [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2024	41	72	41
2023	51	47	63
2022	35	22	29
2021	17	4	6
2020	3	1	2
Prior	1	1	1
Revolving Loans Amortized Cost Basis	8	7	8
Total	156	154	150
Pass [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2024	1,615	2,488	1,226
2023	1,749	2,007	2,562
2022	1,721	1,041	1,196
2021	937	499	573
2020	418	214	245
Prior	697	578	655
Revolving Loans Amortized Cost Basis	163	145	146
Total	7,300	6,972	6,603
Pass [Member] | C&I [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2024	340	720	333
2023	431	276	468
2022	201	73	105
2021	65	36	44
2020	29	14	18
Prior	33	23	26
Total	1,099	1,142	994
Pass [Member] | Municipal [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2024	148	25	11
2023	31	83	84
2022	80	15	17
2021	14	10	14
2020	9	1	1
Prior	76	80	87
Total	358	214	214
Pass [Member] | Agriculture [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2024	38	63	30
2023	36	15	42
2022	5	4	5
2021	3	1	2
2020	1	1	1
Total	83	84	80
Pass [Member] | Construction & Development [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2024	304	515	242
2023	350	311	498
2022	215	78	103
2021	60	20	24
2020	17	9	11
Prior	13	6	12
Total	959	939	890
Pass [Member] | Farm [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2024	63	101	63
2023	51	111	126
2022	78	73	78
2021	68	24	26
2020	22	8	9
Prior	27	22	26
Total	309	339	328
Pass [Member] | Non-Owner Occupied CRE [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2024	118	167	101
2023	88	232	234
2022	241	172	185
2021	165	106	125
2020	72	41	46
Prior	102	73	88
Total	786	791	779
Pass [Member] | Owner Occupied CRE [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2024	62	154	67
2023	148	305	321
2022	293	217	240
2021	200	114	121
2020	105	62	68
Prior	175	142	156
Total	983	994	973
Pass [Member] | Residential [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2024	286	477	228
2023	409	415	461
2022	407	313	335
2021	292	158	172
2020	143	67	73
Prior	264	229	255
Revolving Loans Amortized Cost Basis	155	138	138
Total	1,956	1,797	1,662
Pass [Member] | Auto [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2024	215	195	110
2023	155	212	265
2022	166	74	99
2021	53	26	39
2020	17	10	16
Prior	6	2	4
Total	612	519	533
Pass [Member] | Non-Auto [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2024	41	71	41
2023	50	47	63
2022	35	22	29
2021	17	4	6
2020	3	1	2
Prior	1	1	1
Revolving Loans Amortized Cost Basis	8	7	8
Total	155	153	150
Special Mention [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2024	30	11	16
2023	4	11	13
2022	4	7	4
2021	11	2	7
2020	1	2	19
Prior	7	6	6
Revolving Loans Amortized Cost Basis	1	1	1
Total	58	40	66
Special Mention [Member] | C&I [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2024	22	1	8
2023		1	1
2022		0
2020		1	1
Total	22	3	10
Special Mention [Member] | Municipal [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020			1
Total			1
Special Mention [Member] | Agriculture [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2023			1
Total	0		1
Special Mention [Member] | Construction & Development [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2024	6	8	8
2023	2	2	4
2022	2
Total	10	10	12
Special Mention [Member] | Farm [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2021			5
Total	0		5
Special Mention [Member] | Non-Owner Occupied CRE [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2023		5	5
2022		1	1
2021	1
2020			11
Prior	3	2	2
Total	4	8	19
Special Mention [Member] | Owner Occupied CRE [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2024	2	1
2023	1	1
2022		4
2021	8	0
2020		1	6
Prior	2	1	1
Total	13	8	7
Special Mention [Member] | Residential [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2024		1
2023	1	2	2
2022	2	2	3
2021	2	2	2
2020	1
Prior	2	3	3
Revolving Loans Amortized Cost Basis	1	1	1
Total	9	11	11
Substandard [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2024	24	32	10
2023	15	18	30
2022	45	14	17
2021	20	17	7
2020	16	24	10
Prior	39	29	33
Revolving Loans Amortized Cost Basis	3	3	2
Total	162	137	109
Substandard [Member] | C&I [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2024	11	12	3
2023	3	2	7
2022	2	2	4
2021	2	1	2
2020	1	1
Prior	2	2	2
Total	21	20	18
Substandard [Member] | Municipal [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2022		1	1
2021	1
Total	1	1	1
Substandard [Member] | Agriculture [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2024	3	1
2023			1
Total	3	1	1
Substandard [Member] | Construction & Development [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2024	7	9	4
2023	3	4	8
2022	1	1	1
2021	6
Total	17	14	13
Substandard [Member] | Farm [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2023	1		1
2022	4		1
2021		5
2020	5
Prior		1	1
Total	10	6	3
Substandard [Member] | Non-Owner Occupied CRE [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2024	1	2
2023	1	1	1
2022	1	2	4
2021	3	7	1
2020	5	13	2
Prior	15	4	5
Total	26	29	13
Substandard [Member] | Owner Occupied CRE [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2024	1	3	2
2023	2	6	5
2022	32	4	1
2021	4	0	1
2020	2	7	6
Prior	13	15	17
Total	54	35	32
Substandard [Member] | Residential [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2024	1	4	1
2023	4	4	6
2022	4	3	4
2021	2	3	3
2020	3	3	2
Prior	9	7	8
Revolving Loans Amortized Cost Basis	3	3	2
Total	26	27	26
Substandard [Member] | Auto [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2023		1	1
2022	1	1	1
2021	2	1
Total	3	3	$ 2
Substandard [Member] | Non-Auto [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2024		1
2023	1
Total	$ 1	$ 1