Mortgage Servicing Rights - MSRs and Related Characteristics by Portfolio (Detail) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2022 USD ($) BasisPoint Multiple	Dec. 31, 2021 USD ($) BasisPoint Multiple	Jun. 30, 2022 USD ($)	Sep. 30, 2021 USD ($)	Jun. 30, 2021 USD ($)	Dec. 31, 2020 USD ($)
Servicing Assets at Fair Value [Line Items]
Fair value	$ 3,869	$ 2,953	$ 3,707	$ 2,910	$ 2,713	$ 2,210
Mortgage Servicing Rights [Member]
Servicing Assets at Fair Value [Line Items]
Servicing portfolio	225,185	218,953
Fair value	$ 3,869	$ 2,953
Value (bps) | BasisPoint	172	135
Weighted-average servicing fees (bps) | BasisPoint	33	32
Multiple (value/servicing fees)	5.26	4.18
Weighted-average note rate	3.60%	3.56%
Weighted-average age (in years)	3 years 9 months 18 days	3 years 8 months 12 days
Prepayment (constant prepayment rate)	6.80%	10.30%
Weighted-average expected life (in years)	8 years 3 months 18 days	6 years 8 months 12 days
Weighted-average option adjusted spread	5.90%	6.60%
HFA [Member] | Mortgage Servicing Rights [Member]
Servicing Assets at Fair Value [Line Items]
Servicing portfolio	$ 42,952	$ 40,652
Fair value	$ 731	$ 527
Value (bps) | BasisPoint	170	130
Weighted-average servicing fees (bps) | BasisPoint	36	36
Multiple (value/servicing fees) | Multiple	4.73	3.63
Weighted-average note rate	4.08%	4.07%
Weighted-average age (in years)	4 years	3 years 9 months 18 days
Prepayment (constant prepayment rate)	7.10%	11.50%
Weighted-average expected life (in years)	8 years 10 months 24 days	6 years 6 months
Weighted-average option adjusted spread	6.90%	7.30%
Government Insured [Member] | Mortgage Servicing Rights [Member]
Servicing Assets at Fair Value [Line Items]
Servicing portfolio	$ 21,800	$ 21,919
Fair value	$ 440	$ 308
Value (bps) | BasisPoint	202	141
Weighted-average servicing fees (bps) | BasisPoint	42	41
Multiple (value/servicing fees) | Multiple	4.8	3.43
Weighted-average note rate	3.73%	3.70%
Weighted-average age (in years)	6 years	5 years 10 months 24 days
Prepayment (constant prepayment rate)	8.00%	13.20%
Weighted-average expected life (in years)	7 years 8 months 12 days	5 years 7 months 6 days
Weighted-average option adjusted spread	6.50%	7.30%
Conventional [Member] | Mortgage Servicing Rights [Member]
Servicing Assets at Fair Value [Line Items]
Servicing portfolio	$ 160,433	$ 156,382
Fair value	$ 2,698	$ 2,118
Value (bps) | BasisPoint	168	135
Weighted-average servicing fees (bps) | BasisPoint	31	30
Multiple (value/servicing fees) | Multiple	5.51	4.5
Weighted-average note rate	3.45%	3.41%
Weighted-average age (in years)	3 years 6 months	3 years 3 months 18 days
Prepayment (constant prepayment rate)	6.50%	9.60%
Weighted-average expected life (in years)	8 years 2 months 12 days	6 years 10 months 24 days
Weighted-average option adjusted spread	5.60%	6.30%