Loans And Allowance For Credit 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	Dec. 31, 2021	Dec. 31, 2020
Financing Receivable Recorded Investment [Line Items]
2021-2020	$ 2,585	$ 2,418
2020-2019	1,027	832
2019-2018	499	571
2018-2017	353	350
2017-2016	236	279
Prior	579	619
Revolving Loans Amort Cost Basis	110	102
Total Past Due	5,389	5,171
Agricultural [Member]
Financing Receivable Recorded Investment [Line Items]
2021-2020	73	63
2020-2019	9	19
2019-2018	6	9
2018-2017	6	3
2017-2016	3	1
Prior	1
Total Past Due	98	95
Pass [Member]
Financing Receivable Recorded Investment [Line Items]
2021-2020	2,548	2,356
2020-2019	1,005	804
2019-2018	471	540
2018-2017	332	320
2017-2016	217	273
Prior	548	580
Revolving Loans Amort Cost Basis	107	100
Total Past Due	5,228	4,973
Pass [Member] | Agricultural [Member]
Financing Receivable Recorded Investment [Line Items]
2021-2020	69	57
2020-2019	8	19
2019-2018	6	9
2018-2017	6	3
2017-2016	3	1
Prior	1
Total Past Due	93	89
Special Mention [Member]
Financing Receivable Recorded Investment [Line Items]
2021-2020	12	20
2020-2019	8	12
2019-2018	17	4
2018-2017	1	14
2017-2016	9	3
Prior	7	4
Revolving Loans Amort Cost Basis	1
Total Past Due	55	57
Substandard [Member]
Financing Receivable Recorded Investment [Line Items]
2021-2020	25	42
2020-2019	14	16
2019-2018	11	27
2018-2017	20	16
2017-2016	10	3
Prior	24	35
Revolving Loans Amort Cost Basis	2	2
Total Past Due	106	141
Substandard [Member] | Agricultural [Member]
Financing Receivable Recorded Investment [Line Items]
2021-2020	4	6
2020-2019	1
Total Past Due	5	6
C&I [Member]
Financing Receivable Recorded Investment [Line Items]
2021-2020	537	895
2020-2019	183	107
2019-2018	57	74
2018-2017	32	29
2017-2016	17	10
Prior	11	16
Total Past Due	837	1,131
C&I [Member] | Pass [Member]
Financing Receivable Recorded Investment [Line Items]
2021-2020	526	874
2020-2019	178	101
2019-2018	52	70
2018-2017	29	28
2017-2016	17	10
Prior	11	16
Total Past Due	813	1,099
C&I [Member] | Special Mention [Member]
Financing Receivable Recorded Investment [Line Items]
2021-2020	4	9
2020-2019	1	2
2019-2018	4
2018-2017		1
Total Past Due	9	12
C&I [Member] | Substandard [Member]
Financing Receivable Recorded Investment [Line Items]
2021-2020	7	12
2020-2019	4	4
2019-2018	1	4
2018-2017	3
Total Past Due	15	20
Muncipal [Member]
Financing Receivable Recorded Investment [Line Items]
2021-2020	39	28
2020-2019	15	19
2019-2018	6	29
2018-2017	22	19
2017-2016	17	14
Prior	79	72
Total Past Due	178	181
Muncipal [Member] | Pass [Member]
Financing Receivable Recorded Investment [Line Items]
2021-2020	39	26
2020-2019	15	19
2019-2018	6	29
2018-2017	22	14
2017-2016	17	13
Prior	79	71
Total Past Due	178	172
Muncipal [Member] | Substandard [Member]
Financing Receivable Recorded Investment [Line Items]
2021-2020		2
2018-2017		5
2017-2016		1
Prior		1
Total Past Due		9
Construction & Development [Member]
Financing Receivable Recorded Investment [Line Items]
2021-2020	561	377
2020-2019	136	102
2019-2018	24	36
2018-2017	14	22
2017-2016	7	7
Prior	8	10
Total Past Due	750	554
Construction & Development [Member] | Pass [Member]
Financing Receivable Recorded Investment [Line Items]
2021-2020	557	371
2020-2019	134	97
2019-2018	24	36
2018-2017	14	19
2017-2016	7	7
Prior	8	9
Total Past Due	744	539
Construction & Development [Member] | Special Mention [Member]
Financing Receivable Recorded Investment [Line Items]
2021-2020	2	2
2020-2019		4
Total Past Due	2	6
Construction & Development [Member] | Substandard [Member]
Financing Receivable Recorded Investment [Line Items]
2021-2020	2	4
2020-2019	2	1
2018-2017		3
Prior		1
Total Past Due	4	9
Farm [Member]
Financing Receivable Recorded Investment [Line Items]
2021-2020	118	64
2020-2019	43	23
2019-2018	15	18
2018-2017	11	12
2017-2016	7	11
Prior	23	24
Total Past Due	217	152
Farm [Member] | Pass [Member]
Financing Receivable Recorded Investment [Line Items]
2021-2020	117	57
2020-2019	42	22
2019-2018	15	18
2018-2017	10	11
2017-2016	7	11
Prior	23	23
Total Past Due	214	142
Farm [Member] | Substandard [Member]
Financing Receivable Recorded Investment [Line Items]
2021-2020	1	7
2020-2019	1	1
2018-2017	1	1
Prior		1
Total Past Due	3	10
Non - Owner Occupied CRE [Member]
Financing Receivable Recorded Investment [Line Items]
2021-2020	214	198
2020-2019	130	119
2019-2018	92	94
2018-2017	57	52
2017-2016	41	56
Prior	90	99
Total Past Due	624	618
Non - Owner Occupied CRE [Member] | Pass [Member]
Financing Receivable Recorded Investment [Line Items]
2021-2020	214	197
2020-2019	128	117
2019-2018	77	93
2018-2017	56	44
2017-2016	31	55
Prior	84	88
Total Past Due	590	594
Non - Owner Occupied CRE [Member] | Special Mention [Member]
Financing Receivable Recorded Investment [Line Items]
2021-2020		1
2020-2019	1
2019-2018	12	1
2018-2017	0	8
2017-2016	7	1
Prior	3
Total Past Due	23	11
Non - Owner Occupied CRE [Member] | Substandard [Member]
Financing Receivable Recorded Investment [Line Items]
2020-2019	1	2
2019-2018	3
2018-2017	1
2017-2016	3
Prior	3	11
Total Past Due	11	13
Owner Occupied CRE [Member]
Financing Receivable Recorded Investment [Line Items]
2021-2020	260	186
2020-2019	147	141
2019-2018	118	127
2018-2017	103	83
2017-2016	65	67
Prior	129	143
Total Past Due	822	747
Owner Occupied CRE [Member] | Pass [Member]
Financing Receivable Recorded Investment [Line Items]
2021-2020	250	176
2020-2019	143	132
2019-2018	114	105
2018-2017	90	75
2017-2016	59	65
Prior	117	132
Total Past Due	773	685
Owner Occupied CRE [Member] | Special Mention [Member]
Financing Receivable Recorded Investment [Line Items]
2021-2020	2	5
2020-2019	2	5
2019-2018	1	2
2018-2017		4
2017-2016	1	1
Prior	1	1
Total Past Due	7	18
Owner Occupied CRE [Member] | Substandard [Member]
Financing Receivable Recorded Investment [Line Items]
2021-2020	8	5
2020-2019	2	4
2019-2018	3	20
2018-2017	13	4
2017-2016	5	1
Prior	11	10
Total Past Due	42	44
Residential [Member]
Financing Receivable Recorded Investment [Line Items]
2021-2020	483	381
2020-2019	237	176
2019-2018	118	138
2018-2017	87	105
2017-2016	71	103
Prior	235	250
Revolving Loans Amort Cost Basis	103	95
Total Past Due	1,334	1,248
Residential [Member] | Pass [Member]
Financing Receivable Recorded Investment [Line Items]
2021-2020	477	373
2020-2019	230	172
2019-2018	115	134
2018-2017	84	101
2017-2016	68	101
Prior	222	237
Revolving Loans Amort Cost Basis	100	93
Total Past Due	1,296	1,211
Residential [Member] | Special Mention [Member]
Financing Receivable Recorded Investment [Line Items]
2021-2020	3	3
2020-2019	4	1
2019-2018		1
2018-2017	1	1
2017-2016	1	1
Prior	3	3
Revolving Loans Amort Cost Basis	1
Total Past Due	13	10
Residential [Member] | Substandard [Member]
Financing Receivable Recorded Investment [Line Items]
2021-2020	3	5
2020-2019	3	3
2019-2018	3	3
2018-2017	2	3
2017-2016	2	1
Prior	10	10
Revolving Loans Amort Cost Basis	2	2
Total Past Due	25	27
Auto [Member]
Financing Receivable Recorded Investment [Line Items]
2021-2020	219	178
2020-2019	105	105
2019-2018	55	39
2018-2017	17	21
2017-2016	7	9
Prior	2	2
Total Past Due	405	354
Auto [Member] | Pass [Member]
Financing Receivable Recorded Investment [Line Items]
2021-2020	218	177
2020-2019	105	104
2019-2018	54	39
2018-2017	17	21
2017-2016	7	9
Prior	2	2
Total Past Due	403	352
Auto [Member] | Special Mention [Member]
Financing Receivable Recorded Investment [Line Items]
2021-2020	1
Total Past Due	1
Auto [Member] | Substandard [Member]
Financing Receivable Recorded Investment [Line Items]
2021-2020		1
2020-2019		1
2019-2018	1
Total Past Due	1	2
Non - Auto [Member]
Financing Receivable Recorded Investment [Line Items]
2021-2020	81	48
2020-2019	22	21
2019-2018	8	7
2018-2017	4	4
2017-2016	1	1
Prior	1	3
Revolving Loans Amort Cost Basis	7	7
Total Past Due	124	91
Non - Auto [Member] | Pass [Member]
Financing Receivable Recorded Investment [Line Items]
2021-2020	81	48
2020-2019	22	21
2019-2018	8	7
2018-2017	4	4
2017-2016	1	1
Prior	1	2
Revolving Loans Amort Cost Basis	7	7
Total Past Due	$ 124	90
Non - Auto [Member] | Substandard [Member]
Financing Receivable Recorded Investment [Line Items]
Prior		1
Total Past Due		$ 1