Mortgage Servicing Rights - MSRs and Related Characteristics by Portfolio (Detail) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2016 USD ($) BasisPoint Multiple	Dec. 31, 2015 USD ($) BasisPoint Multiple	Mar. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Servicing Assets at Fair Value [Line Items]
Fair value	$ 2,222	$ 2,512	$ 2,250	$ 2,338
Mortgage Servicing Rights [Member]
Servicing Assets at Fair Value [Line Items]
Servicing portfolio	229,748	229,375
Fair value	$ 2,222	$ 2,512
Value (bps) | BasisPoint	97	110
Weighted-average servicing fees (bps) | BasisPoint	29	29
Multiple (value/servicing fees) | Multiple	3.34	3.79
Weighted-average note rate	4.12%	4.13%
Weighted-average age (in years)	3 years 6 months	3 years 4 months 24 days
Weighted-average expected prepayment (constant prepayment rate)	13.90%	11.30%
Weighted-average expected life (in years)	5 years 6 months	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	$ 28,241	$ 26,492
Fair value	$ 314	$ 297
Value (bps) | BasisPoint	111	112
Weighted-average servicing fees (bps) | BasisPoint	36	36
Multiple (value/servicing fees) | Multiple	3.08	3.11
Weighted-average note rate	4.45%	4.46%
Weighted-average age (in years)	3 years 1 month 6 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	11.80%	11.80%
Government [Member] | Mortgage Servicing Rights [Member]
Servicing Assets at Fair Value [Line Items]
Servicing portfolio	$ 39,921	$ 40,350
Fair value	$ 385	$ 443
Value (bps) | BasisPoint	96	110
Weighted-average servicing fees (bps) | BasisPoint	34	34
Multiple (value/servicing fees) | Multiple	2.82	3.24
Weighted-average note rate	4.06%	4.08%
Weighted-average age (in years)	3 years 8 months 12 days	3 years 7 months 6 days
Weighted-average expected prepayment (constant prepayment rate)	17.20%	13.90%
Weighted-average expected life (in years)	4 years 9 months 18 days	5 years 8 months 12 days
Weighted-average discount rate	11.20%	11.20%
Conventional [Member] | Mortgage Servicing Rights [Member]
Servicing Assets at Fair Value [Line Items]
Servicing portfolio	$ 161,586	$ 162,533
Fair value	$ 1,523	$ 1,772
Value (bps) | BasisPoint	94	109
Weighted-average servicing fees (bps) | BasisPoint	27	27
Multiple (value/servicing fees) | Multiple	3.48	4.04
Weighted-average note rate	4.08%	4.09%
Weighted-average age (in years)	3 years 6 months	3 years 4 months 24 days
Weighted-average expected prepayment (constant prepayment rate)	13.30%	10.40%
Weighted-average expected life (in years)	5 years 6 months	6 years 7 months 6 days
Weighted-average discount rate	9.40%	9.40%