Mortgage Servicing Rights - MSRs and Related Characteristics by Portfolio (Detail) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2021 USD ($) BasisPoint Multiple	Dec. 31, 2020 USD ($) Multiple BasisPoint	Mar. 31, 2021 USD ($)	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Servicing Assets at Fair Value [Line Items]
Fair value	$ 2,713	$ 2,210	$ 2,787	$ 1,840	$ 1,887	$ 2,546
Mortgage Servicing Rights [Member]
Servicing Assets at Fair Value [Line Items]
Servicing portfolio	211,922	208,955
Fair value	$ 2,713	$ 2,210
Value (bps) | BasisPoint	128	106
Weighted-average servicing fees (bps) | BasisPoint	32	32
Multiple (value/servicing fees) | Multiple	3.96	3.26
Weighted-average note rate	3.70%	3.92%
Weighted-average age (in years)	3 years 10 months 24 days	4 years 3 months 18 days
Weighted-average expected prepayment (constant prepayment rate)	11.10%	14.40%
Weighted-average expected life (in years)	6 years 6 months	5 years 4 months 24 days
Weighted-average option adjusted spread	6.80%	6.60%
HFA [Member] | Mortgage Servicing Rights [Member]
Servicing Assets at Fair Value [Line Items]
Servicing portfolio	$ 39,564	$ 40,396
Fair value	$ 478	$ 406
Value (bps) | BasisPoint	121	101
Weighted-average servicing fees (bps) | BasisPoint	35	35
Multiple (value/servicing fees) | Multiple	3.40	2.87
Weighted-average note rate	4.23%	4.43%
Weighted-average age (in years)	3 years 9 months 18 days	3 years 9 months 18 days
Weighted-average expected prepayment (constant prepayment rate)	12.00%	14.10%
Weighted-average expected life (in years)	6 years 4 months 24 days	5 years 7 months 6 days
Weighted-average option adjusted spread	7.70%	7.70%
Government Insured [Member] | Mortgage Servicing Rights [Member]
Servicing Assets at Fair Value [Line Items]
Servicing portfolio	$ 22,698	$ 25,474
Fair value	$ 285	$ 261
Value (bps) | BasisPoint	126	102
Weighted-average servicing fees (bps) | BasisPoint	40	40
Multiple (value/servicing fees) | Multiple	3.15	2.56
Weighted-average note rate	3.82%	3.91%
Weighted-average age (in years)	5 years 10 months 24 days	5 years 7 months 6 days
Weighted-average expected prepayment (constant prepayment rate)	14.40%	18.00%
Weighted-average expected life (in years)	5 years 2 months 12 days	4 years 3 months 18 days
Weighted-average option adjusted spread	7.30%	7.30%
Conventional [Member] | Mortgage Servicing Rights [Member]
Servicing Assets at Fair Value [Line Items]
Servicing portfolio	$ 149,660	$ 143,085
Fair value	$ 1,950	$ 1,543
Value (bps) | BasisPoint	130	108
Weighted-average servicing fees (bps) | BasisPoint	30	30
Multiple (value/servicing fees) | Multiple	4.30	3.55
Weighted-average note rate	3.54%	3.78%
Weighted-average age (in years)	3 years 7 months 6 days	4 years 2 months 12 days
Weighted-average expected prepayment (constant prepayment rate)	10.30%	13.80%
Weighted-average expected life (in years)	6 years 8 months 12 days	5 years 6 months
Weighted-average option adjusted spread	6.40%	6.20%