Mortgage Servicing Rights - MSRs and Related Characteristics by Portfolio (Detail) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2017 USD ($) BasisPoint Multiple	Dec. 31, 2016 USD ($) BasisPoint Multiple	Mar. 31, 2017 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Servicing Assets at Fair Value [Line Items]
Fair value	$ 2,582	$ 2,591	$ 2,642	$ 2,056	$ 2,222	$ 2,512
Mortgage Servicing Rights [Member]
Servicing Assets at Fair Value [Line Items]
Servicing portfolio	230,690	230,047
Fair value	$ 2,582	$ 2,591
Value (bps) | BasisPoint	112	113
Weighted-average servicing fees (bps) | BasisPoint	30	30
Multiple (value/servicing fees) | Multiple	3.73	3.77
Weighted-average note rate	4.07%	4.06%
Weighted-average age (in years)	3 years 9 months 18 days	3 years 8 months 12 days
Weighted-average expected prepayment (constant prepayment rate)	10.20%	10.00%
Weighted-average expected life (in years)	6 years 10 months 25 days	7 years
Weighted-average option adjusted spread	8.00%	8.00%
HFA [Member] | Mortgage Servicing Rights [Member]
Servicing Assets at Fair Value [Line Items]
Servicing portfolio	$ 38,104	$ 34,746
Fair value	$ 425	$ 398
Value (bps) | BasisPoint	112	115
Weighted-average servicing fees (bps) | BasisPoint	35	36
Multiple (value/servicing fees) | Multiple	3.20	3.19
Weighted-average note rate	4.39%	4.37%
Weighted-average age (in years)	2 years 10 months 25 days	2 years 10 months 24 days
Weighted-average expected prepayment (constant prepayment rate)	9.60%	9.40%
Weighted-average expected life (in years)	7 years 9 months 18 days	8 years
Weighted-average option adjusted spread	9.90%	9.90%
Government Insured [Member] | Mortgage Servicing Rights [Member]
Servicing Assets at Fair Value [Line Items]
Servicing portfolio	$ 37,314	$ 37,530
Fair value	$ 420	$ 422
Value (bps) | BasisPoint	113	112
Weighted-average servicing fees (bps) | BasisPoint	34	34
Multiple (value/servicing fees) | Multiple	3.32	3.29
Weighted-average note rate	3.93%	3.95%
Weighted-average age (in years)	4 years	3 years 9 months 18 days
Weighted-average expected prepayment (constant prepayment rate)	11.70%	11.30%
Weighted-average expected life (in years)	6 years 6 months	6 years 9 months 18 days
Weighted-average option adjusted spread	9.20%	9.20%
Conventional [Member] | Mortgage Servicing Rights [Member]
Servicing Assets at Fair Value [Line Items]
Servicing portfolio	$ 155,272	$ 157,771
Fair value	$ 1,737	$ 1,771
Value (bps) | BasisPoint	112	112
Weighted-average servicing fees (bps) | BasisPoint	27	27
Multiple (value/servicing fees) | Multiple	4.15	4.15
Weighted-average note rate	4.02%	4.02%
Weighted-average age (in years)	3 years 10 months 25 days	3 years 9 months 18 days
Weighted-average expected prepayment (constant prepayment rate)	10.00%	9.80%
Weighted-average expected life (in years)	6 years 9 months 18 days	6 years 10 months 24 days
Weighted-average option adjusted spread	7.20%	7.20%