Mortgage Servicing Rights - MSRs and Related Characteristics by Portfolio (Detail) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2020 USD ($) BasisPoint Multiple	Dec. 31, 2019 USD ($) BasisPoint Multiple	Mar. 31, 2020 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Servicing Assets at Fair Value [Line Items]
Fair value	$ 1,840	$ 2,546	$ 1,887	$ 2,458	$ 2,656	$ 2,791
Mortgage Servicing Rights [Member]
Servicing Assets at Fair Value [Line Items]
Servicing portfolio	217,650	223,518
Fair value	$ 1,840	$ 2,546
Value (bps) | BasisPoint	85	114
Weighted-average servicing fees (bps) | BasisPoint	32	31
Multiple (value/servicing fees) | Multiple	2.66	3.67
Weighted-average note rate	4.11%	4.17%
Weighted-average age (in years)	4 years 8 months 12 days	4 years 7 months 6 days
Weighted-average expected prepayment (constant prepayment rate)	20.20%	12.40%
Weighted-average expected life (in years)	4 years 1 month 6 days	6 years
Weighted-average option adjusted spread	6.10%	7.30%
HFA [Member] | Mortgage Servicing Rights [Member]
Servicing Assets at Fair Value [Line Items]
Servicing portfolio	$ 44,216	$ 44,906
Fair value	$ 375	$ 486
Value (bps) | BasisPoint	85	108
Weighted-average servicing fees (bps) | BasisPoint	35	34
Multiple (value/servicing fees) | Multiple	2.45	3.15
Weighted-average note rate	4.59%	4.65%
Weighted-average age (in years)	3 years 9 months 18 days	3 years 8 months 12 days
Weighted-average expected prepayment (constant prepayment rate)	16.50%	12.20%
Weighted-average expected life (in years)	5 years 1 month 6 days	6 years 6 months
Weighted-average option adjusted spread	7.10%	8.40%
Government Insured [Member] | Mortgage Servicing Rights [Member]
Servicing Assets at Fair Value [Line Items]
Servicing portfolio	$ 33,064	$ 35,302
Fair value	$ 327	$ 451
Value (bps) | BasisPoint	99	128
Weighted-average servicing fees (bps) | BasisPoint	40	39
Multiple (value/servicing fees) | Multiple	2.48	3.29
Weighted-average note rate	3.95%	3.99%
Weighted-average age (in years)	5 years 2 months 12 days	4 years 10 months 24 days
Weighted-average expected prepayment (constant prepayment rate)	19.00%	13.70%
Weighted-average expected life (in years)	4 years 3 months 18 days	5 years 8 months 12 days
Weighted-average option adjusted spread	6.70%	7.90%
Conventional [Member] | Mortgage Servicing Rights [Member]
Servicing Assets at Fair Value [Line Items]
Servicing portfolio	$ 140,370	$ 143,310
Fair value	$ 1,138	$ 1,609
Value (bps) | BasisPoint	81	112
Weighted-average servicing fees (bps) | BasisPoint	29	28
Multiple (value/servicing fees) | Multiple	2.79	4.00
Weighted-average note rate	4.00%	4.07%
Weighted-average age (in years)	4 years 9 months 18 days	4 years 9 months 18 days
Weighted-average expected prepayment (constant prepayment rate)	21.70%	12.20%
Weighted-average expected life (in years)	3 years 8 months 12 days	5 years 10 months 24 days
Weighted-average option adjusted spread	5.60%	6.90%