Mortgage Servicing Rights - MSRs and Related Characteristics by Portfolio (Detail) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2015 USD ($) BasisPoint Multiple	Dec. 31, 2014 USD ($) BasisPoint Multiple	Mar. 31, 2015 USD ($)	Jun. 30, 2014 USD ($)	Mar. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Servicing Assets at Fair Value [Line Items]
Fair value	$ 2,481	$ 2,338	$ 2,250	$ 2,412	$ 2,618	$ 2,680
Mortgage Servicing Rights [Member]
Servicing Assets at Fair Value [Line Items]
Servicing portfolio	223,175	222,797
Fair value	$ 2,481	$ 2,338
Value (bps) | BasisPoint	111	105
Weighted-average servicing fees (bps) | BasisPoint	29	29
Multiple (value/servicing fees) | Multiple	3.83	3.62
Weighted-average note rate	4.15%	4.19%
Weighted-average age (in years)	3 years 3 months 18 days	3 years 2 months 12 days
Weighted-average expected prepayment (constant prepayment rate)	11.00%	12.10%
Weighted-average expected life (in years)	6 years 7 months 6 days	6 years 3 months 18 days
Weighted-average discount rate	10.10%	10.10%
HFA [Member] | Mortgage Servicing Rights [Member]
Servicing Assets at Fair Value [Line Items]
Servicing portfolio	$ 22,226	$ 19,706
Fair value	$ 243	$ 213
Value (bps) | BasisPoint	109	108
Weighted-average servicing fees (bps) | BasisPoint	36	37
Multiple (value/servicing fees) | Multiple	3.03	2.92
Weighted-average note rate	4.51%	4.58%
Weighted-average age (in years)	3 years 4 months 24 days	3 years 7 months 6 days
Weighted-average expected prepayment (constant prepayment rate)	12.90%	12.80%
Weighted-average expected life (in years)	6 years 1 month 6 days	6 years 2 months 12 days
Weighted-average discount rate	11.80%	11.90%
Government [Member] | Mortgage Servicing Rights [Member]
Servicing Assets at Fair Value [Line Items]
Servicing portfolio	$ 40,017	$ 40,471
Fair value	$ 444	$ 426
Value (bps) | BasisPoint	111	105
Weighted-average servicing fees (bps) | BasisPoint	33	33
Multiple (value/servicing fees) | Multiple	3.36	3.18
Weighted-average note rate	4.13%	4.18%
Weighted-average age (in years)	3 years 4 months 24 days	3 years 2 months 12 days
Weighted-average expected prepayment (constant prepayment rate)	13.70%	14.80%
Weighted-average expected life (in years)	5 years 9 months 18 days	5 years 6 months
Weighted-average discount rate	11.30%	11.20%
Conventional [Member] | Mortgage Servicing Rights [Member]
Servicing Assets at Fair Value [Line Items]
Servicing portfolio	$ 160,932	$ 162,620
Fair value	$ 1,794	$ 1,699
Value (bps) | BasisPoint	111	104
Weighted-average servicing fees (bps) | BasisPoint	27	27
Multiple (value/servicing fees) | Multiple	4.11	3.85
Weighted-average note rate	4.11%	4.14%
Weighted-average age (in years)	3 years 3 months 18 days	3 years 1 month 6 days
Weighted-average expected prepayment (constant prepayment rate)	10.10%	11.40%
Weighted-average expected life (in years)	6 years 9 months 18 days	6 years 6 months
Weighted-average discount rate	9.60%	9.60%