Mortgage Servicing Rights - MSRs and Related Characteristics by Portfolio (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2015 Multiple BasisPoint	Dec. 31, 2014 Multiple BasisPoint	Mar. 31, 2014	Dec. 31, 2013
Servicing Assets at Fair Value [Line Items]
Fair value	$ 2,250	$ 2,338	$ 2,618	$ 2,680
Mortgage Servicing Rights [Member]
Servicing Assets at Fair Value [Line Items]
Servicing portfolio	222,965	222,797
Fair value	2,250	2,338
Value (bps)	101	105
Weighted-average servicing fees (bps)	29	29
Multiple (value/servicing fees)	3.48	3.62
Weighted-average note rate	4.18%	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)	13.20%	12.10%
Weighted-average expected life (in years)	5 years 9 months 18 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	21,055	19,706
Fair value	228	213
Value (bps)	108	108
Weighted-average servicing fees (bps)	36	37
Multiple (value/servicing fees)	3.00	2.92
Weighted-average note rate	4.54%	4.58%
Weighted-average age (in years)	3 years 6 months	3 years 7 months 6 days
Weighted-average expected prepayment (constant prepayment rate)	13.00%	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	40,539	40,471
Fair value	411	426
Value (bps)	101	105
Weighted-average servicing fees (bps)	33	33
Multiple (value/servicing fees)	3.06	3.18
Weighted-average note rate	4.16%	4.18%
Weighted-average age (in years)	3 years 3 months 18 days	3 years 2 months 12 days
Weighted-average expected prepayment (constant prepayment rate)	16.00%	14.80%
Weighted-average expected life (in years)	5 years 1 month 6 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	161,371	162,620
Fair value	$ 1,611	$ 1,699
Value (bps)	100	104
Weighted-average servicing fees (bps)	27	27
Multiple (value/servicing fees)	3.70	3.85
Weighted-average note rate	4.14%	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)	12.50%	11.40%
Weighted-average expected life (in years)	6 years	6 years 6 months
Weighted-average discount rate	9.60%	9.60%