Mortgage Servicing Rights - MSRs and Related Characteristics by Portfolio (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2025	Dec. 31, 2024	Mar. 31, 2024	Dec. 31, 2023
Servicing Assets at Fair Value [Line Items]
Fair value	$ 3,312	$ 3,369	$ 3,462	$ 3,377
MSR portfolio
Servicing Assets at Fair Value [Line Items]
Servicing portfolio	216,435	216,374
Fair value	$ 3,312	$ 3,369
Value (bps)	1.53%	1.56%
Weighted-average servicing fees (bps)	0.30%	0.30%
Multiple (value/servicing fees)	5.08	5.17
Weighted-average note rate	4.23%	4.18%
Weighted-average age (in years)	5 years 1 month 6 days	5 years
Weighted-average expected prepayment (constant prepayment rate)	9.00%	8.60%
Weighted-average expected life (in years)	7 years 2 months 12 days	7 years 4 months 24 days
Weighted-average option adjusted spread	5.70%	5.70%
MSR portfolio | HFA
Servicing Assets at Fair Value [Line Items]
Servicing portfolio	$ 54,095	$ 52,807
Fair value	$ 819	$ 856
Value (bps)	1.51%	1.62%
Weighted-average servicing fees (bps)	0.35%	0.35%
Multiple (value/servicing fees)	4.27	4.57
Weighted-average note rate	4.99%	4.92%
Weighted-average age (in years)	4 years 7 months 6 days	4 years 6 months
Weighted-average expected prepayment (constant prepayment rate)	10.50%	9.90%
Weighted-average expected life (in years)	7 years 2 months 12 days	7 years 6 months
Weighted-average option adjusted spread	6.80%	5.80%
MSR portfolio | Government
Servicing Assets at Fair Value [Line Items]
Servicing portfolio	$ 24,797	$ 25,139
Fair value	$ 489	$ 512
Value (bps)	1.97%	2.04%
Weighted-average servicing fees (bps)	0.45%	0.45%
Multiple (value/servicing fees)	4.41	4.56
Weighted-average note rate	4.36%	4.35%
Weighted-average age (in years)	6 years 3 months 18 days	6 years 1 month 6 days
Weighted-average expected prepayment (constant prepayment rate)	10.60%	10.20%
Weighted-average expected life (in years)	6 years 7 months 6 days	6 years 9 months 18 days
Weighted-average option adjusted spread	6.60%	6.20%
MSR portfolio | Conventional
Servicing Assets at Fair Value [Line Items]
Servicing portfolio	$ 137,543	$ 138,428
Fair value	$ 2,004	$ 2,001
Value (bps)	1.46%	1.45%
Weighted-average servicing fees (bps)	0.25%	0.25%
Multiple (value/servicing fees)	5.74	5.69
Weighted-average note rate	3.91%	3.87%
Weighted-average age (in years)	5 years 1 month 6 days	5 years
Weighted-average expected prepayment (constant prepayment rate)	8.20%	7.80%
Weighted-average expected life (in years)	7 years 3 months 18 days	7 years 4 months 24 days
Weighted-average option adjusted spread	5.10%	5.60%