Mortgage Servicing Rights - MSRs and Related Characteristics by Portfolio (Detail) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2016 USD ($) BasisPoint Multiple	Dec. 31, 2015 USD ($) BasisPoint Multiple	Jun. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Dec. 31, 2014 USD ($)
Servicing Assets at Fair Value [Line Items]
Fair value	$ 2,131	$ 2,512	$ 2,056	$ 2,397	$ 2,481	$ 2,338
Mortgage Servicing Rights [Member]
Servicing Assets at Fair Value [Line Items]
Servicing portfolio	229,647	229,375
Fair value	$ 2,131	$ 2,512
Value (bps) | BasisPoint	93	110
Weighted-average servicing fees (bps) | BasisPoint	30	29
Multiple (value/servicing fees) | Multiple	3.10	3.79
Weighted-average note rate	4.10%	4.13%
Weighted-average age (in years)	3 years 8 months 12 days	3 years 4 months 24 days
Weighted-average expected prepayment (constant prepayment rate)	14.70%	11.30%
Weighted-average expected life (in years)	5 years 2 months 12 days	6 years 4 months 24 days
Weighted-average discount rate	10.00%	10.00%
HFA [Member] | Mortgage Servicing Rights [Member]
Servicing Assets at Fair Value [Line Items]
Servicing portfolio	$ 32,757	$ 26,492
Fair value	$ 357	$ 297
Value (bps) | BasisPoint	109	112
Weighted-average servicing fees (bps) | BasisPoint	37	36
Multiple (value/servicing fees) | Multiple	2.95	3.11
Weighted-average note rate	4.41%	4.46%
Weighted-average age (in years)	2 years 10 months 24 days	3 years 1 month 6 days
Weighted-average expected prepayment (constant prepayment rate)	12.70%	12.80%
Weighted-average expected life (in years)	6 years 1 month 6 days	6 years 1 month 6 days
Weighted-average discount rate	11.70%	11.80%
Government [Member] | Mortgage Servicing Rights [Member]
Servicing Assets at Fair Value [Line Items]
Servicing portfolio	$ 38,639	$ 40,350
Fair value	$ 355	$ 443
Value (bps) | BasisPoint	92	110
Weighted-average servicing fees (bps) | BasisPoint	34	34
Multiple (value/servicing fees) | Multiple	2.71	3.24
Weighted-average note rate	4.02%	4.08%
Weighted-average age (in years)	3 years 10 months 24 days	3 years 7 months 6 days
Weighted-average expected prepayment (constant prepayment rate)	18.00%	13.90%
Weighted-average expected life (in years)	4 years 7 months 6 days	5 years 8 months 12 days
Weighted-average discount rate	11.10%	11.20%
Conventional [Member] | Mortgage Servicing Rights [Member]
Servicing Assets at Fair Value [Line Items]
Servicing portfolio	$ 158,251	$ 162,533
Fair value	$ 1,419	$ 1,772
Value (bps) | BasisPoint	90	109
Weighted-average servicing fees (bps) | BasisPoint	27	27
Multiple (value/servicing fees) | Multiple	3.33	4.04
Weighted-average note rate	4.05%	4.09%
Weighted-average age (in years)	3 years 9 months 18 days	3 years 4 months 24 days
Weighted-average expected prepayment (constant prepayment rate)	14.30%	10.40%
Weighted-average expected life (in years)	5 years 2 months 12 days	6 years 7 months 6 days
Weighted-average discount rate	9.40%	9.40%