Mortgage Servicing Rights - MSRs and Related Characteristics by Portfolio (Detail) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2023 USD ($) BasisPoint Multiple	Dec. 31, 2022 USD ($) Multiple BasisPoint	Jun. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)	Jun. 30, 2022 USD ($)	Dec. 31, 2021 USD ($)
Servicing Assets at Fair Value [Line Items]
Fair value	$ 3,582	$ 3,755	$ 3,633	$ 3,869	$ 3,707	$ 2,953
Mortgage Servicing Rights [Member]
Servicing Assets at Fair Value [Line Items]
Servicing portfolio	224,176	239,753
Fair value	$ 3,582	$ 3,755
Value (bps) | BasisPoint	160	157
Weighted-average servicing fees (bps) | BasisPoint	30	30
Multiple (value/servicing fees) | Multiple	5.34	5.2
Weighted-average note rate	3.94%	3.67%
Weighted-average age (in years)	4 years 3 months 18 days	3 years 10 months 24 days
Weighted-average expected prepayment (constant prepayment rate)	8.10%	7.80%
Weighted-average expected life (in years)	7 years 6 months	7 years 8 months 12 days
Weighted-average option adjusted spread	4.90%	5.80%
HFA [Member] | Mortgage Servicing Rights [Member]
Servicing Assets at Fair Value [Line Items]
Servicing portfolio	$ 46,729	$ 44,071
Fair value	$ 795	$ 725
Value (bps) | BasisPoint	170	165
Weighted-average servicing fees (bps) | BasisPoint	36	36
Multiple (value/servicing fees) | Multiple	4.74	4.56
Weighted-average note rate	4.43%	4.16%
Weighted-average age (in years)	4 years 3 months 18 days	4 years
Weighted-average expected prepayment (constant prepayment rate)	8.80%	7.40%
Weighted-average expected life (in years)	7 years 10 months 24 days	8 years 9 months 18 days
Weighted-average option adjusted spread	5.40%	7.60%
Government Insured [Member] | Mortgage Servicing Rights [Member]
Servicing Assets at Fair Value [Line Items]
Servicing portfolio	$ 25,756	$ 23,141
Fair value	$ 539	$ 454
Value (bps) | BasisPoint	209	196
Weighted-average servicing fees (bps) | BasisPoint	44	42
Multiple (value/servicing fees) | Multiple	4.76	4.69
Weighted-average note rate	4.16%	3.81%
Weighted-average age (in years)	5 years 6 months	5 years 8 months 12 days
Weighted-average expected prepayment (constant prepayment rate)	9.40%	8.50%
Weighted-average expected life (in years)	7 years 2 months 12 days	7 years 7 months 6 days
Weighted-average option adjusted spread	5.90%	6.90%
Conventional [Member] | Mortgage Servicing Rights [Member]
Servicing Assets at Fair Value [Line Items]
Servicing portfolio	$ 151,691	$ 172,541
Fair value	$ 2,248	$ 2,576
Value (bps) | BasisPoint	148	149
Weighted-average servicing fees (bps) | BasisPoint	26	27
Multiple (value/servicing fees) | Multiple	5.77	5.52
Weighted-average note rate	3.75%	3.52%
Weighted-average age (in years)	4 years 1 month 6 days	3 years 8 months 12 days
Weighted-average expected prepayment (constant prepayment rate)	7.70%	7.80%
Weighted-average expected life (in years)	7 years 6 months	7 years 6 months
Weighted-average option adjusted spread	4.60%	5.10%