Mortgage Servicing Rights - MSRs and Related Characteristics by Portfolio (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023	Mar. 31, 2023	Dec. 31, 2022
Servicing Assets at Fair Value [Line Items]
Fair value	$ 3,462	$ 3,377	$ 3,724	$ 3,755
MSR portfolio
Servicing Assets at Fair Value [Line Items]
Servicing portfolio	225,486	225,338
Fair value	$ 3,462	$ 3,377
Value (bps)	1.54%	1.50%
Weighted-average servicing fees (bps)	0.30%	0.30%
Multiple (value/servicing fees)	5.11	5.00
Weighted-average note rate	4.08%	4.02%
Weighted-average age (in years)	4 years 7 months 6 days	4 years 4 months 24 days
Weighted-average expected prepayment (constant prepayment rate)	9.30%	9.60%
Weighted-average expected life (in years)	7 years 1 month 6 days	7 years
Weighted-average option adjusted spread	5.00%	4.90%
MSR portfolio | HFA
Servicing Assets at Fair Value [Line Items]
Servicing portfolio	$ 49,275	$ 48,286
Fair value	$ 809	$ 769
Value (bps)	1.64%	1.59%
Weighted-average servicing fees (bps)	0.36%	0.36%
Multiple (value/servicing fees)	4.60	4.45
Weighted-average note rate	4.66%	4.56%
Weighted-average age (in years)	4 years 4 months 24 days	4 years 3 months 18 days
Weighted-average expected prepayment (constant prepayment rate)	10.20%	10.50%
Weighted-average expected life (in years)	7 years 2 months 12 days	7 years 2 months 12 days
Weighted-average option adjusted spread	5.40%	5.40%
MSR portfolio | Government
Servicing Assets at Fair Value [Line Items]
Servicing portfolio	$ 25,961	$ 25,996
Fair value	$ 521	$ 507
Value (bps)	2.01%	1.95%
Weighted-average servicing fees (bps)	0.44%	0.44%
Multiple (value/servicing fees)	4.51	4.41
Weighted-average note rate	4.27%	4.23%
Weighted-average age (in years)	5 years 8 months 12 days	5 years 6 months
Weighted-average expected prepayment (constant prepayment rate)	10.70%	11.10%
Weighted-average expected life (in years)	6 years 7 months 6 days	6 years 6 months
Weighted-average option adjusted spread	5.90%	5.90%
MSR portfolio | Conventional
Servicing Assets at Fair Value [Line Items]
Servicing portfolio	$ 150,250	$ 151,056
Fair value	$ 2,132	$ 2,101
Value (bps)	1.42%	1.39%
Weighted-average servicing fees (bps)	0.26%	0.26%
Multiple (value/servicing fees)	5.52	5.41
Weighted-average note rate	3.85%	3.81%
Weighted-average age (in years)	4 years 6 months	4 years 3 months 18 days
Weighted-average expected prepayment (constant prepayment rate)	8.80%	9.10%
Weighted-average expected life (in years)	7 years 1 month 6 days	7 years
Weighted-average option adjusted spread	4.60%	4.60%