Mortgage Servicing Rights - MSRs and Related Characteristics by Portfolio (Detail) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2022 USD ($) Multiple BasisPoint	Dec. 31, 2021 USD ($) BasisPoint Multiple	Mar. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Servicing Assets at Fair Value [Line Items]
Fair value	$ 3,432	$ 2,953	$ 2,787	$ 2,210
Mortgage Servicing Rights [Member]
Servicing Assets at Fair Value [Line Items]
Servicing portfolio	223,660	218,953
Fair value	$ 3,432	$ 2,953
Value (bps) | BasisPoint	153	135
Weighted-average servicing fees (bps) | BasisPoint	32	32
Multiple (value/servicing fees)	4.75	4.18
Weighted-average note rate	3.53%	3.56%
Weighted-average age (in years)	3 years 8 months 12 days	3 years 8 months 12 days
Prepayment (constant prepayment rate)	8.60%	10.30%
Weighted-average expected life (in years)	7 years 4 months 24 days	6 years 8 months 12 days
Weighted-average option adjusted spread	6.20%	6.60%
HFA [Member] | Mortgage Servicing Rights [Member]
Servicing Assets at Fair Value [Line Items]
Servicing portfolio	$ 41,430	$ 40,652
Fair value	$ 628	$ 527
Value (bps) | BasisPoint	152	130
Weighted-average servicing fees (bps) | BasisPoint	36	36
Multiple (value/servicing fees) | Multiple	4.23	3.63
Weighted-average note rate	4.02%	4.07%
Weighted-average age (in years)	3 years 9 months 18 days	3 years 9 months 18 days
Prepayment (constant prepayment rate)	9.60%	11.50%
Weighted-average expected life (in years)	7 years 6 months	6 years 6 months
Weighted-average option adjusted spread	6.80%	7.30%
Government Insured [Member] | Mortgage Servicing Rights [Member]
Servicing Assets at Fair Value [Line Items]
Servicing portfolio	$ 21,619	$ 21,919
Fair value	$ 365	$ 308
Value (bps) | BasisPoint	169	141
Weighted-average servicing fees (bps) | BasisPoint	41	41
Multiple (value/servicing fees) | Multiple	4.12	3.43
Weighted-average note rate	3.66%	3.70%
Weighted-average age (in years)	6 years	5 years 10 months 24 days
Prepayment (constant prepayment rate)	10.60%	13.20%
Weighted-average expected life (in years)	6 years 6 months	5 years 7 months 6 days
Weighted-average option adjusted spread	6.70%	7.30%
Conventional [Member] | Mortgage Servicing Rights [Member]
Servicing Assets at Fair Value [Line Items]
Servicing portfolio	$ 160,611	$ 156,382
Fair value	$ 2,439	$ 2,118
Value (bps) | BasisPoint	152	135
Weighted-average servicing fees (bps) | BasisPoint	30	30
Multiple (value/servicing fees) | Multiple	5.02	4.50
Weighted-average note rate	3.38%	3.41%
Weighted-average age (in years)	3 years 3 months 18 days	3 years 3 months 18 days
Prepayment (constant prepayment rate)	8.10%	9.60%
Weighted-average expected life (in years)	7 years 6 months	6 years 10 months 24 days
Weighted-average option adjusted spread	6.00%	6.30%