Mortgage Servicing Rights - MSRs and Related Characteristics by Portfolio (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013 BasisPoint Multiple	Jun. 30, 2013	Dec. 31, 2012 BasisPoint Multiple	Sep. 30, 2012	Jun. 30, 2012	Dec. 31, 2011
Servicing Assets at Fair Value [Line Items]
Servicing portfolio	$ 226,727		$ 215,637
Fair value	2,577	2,377	1,700	1,553	1,594	1,519
Value (bps)	114		79
Weighted-average servicing fees (bps)	30		31
Multiple (value/servicing fees)	3.80		2.55
Weighted-average note rate	4.24%		4.54%
Weighted-average age (in years)	2 years 6 months		2 years 7 months 6 days
Weighted-average expected prepayment (constant prepayment rate)	12.30%		20.10%
Weighted-average expected life (in years)	6 years 8 months 12 days		4 years 2 months 12 days
Weighted-average discount rate	10.20%		10.40%
MRBP [Member]
Servicing Assets at Fair Value [Line Items]
Servicing portfolio	15,088		14,143
Fair value	171		154
Value (bps)	113		109
Weighted-average servicing fees (bps)	39		40
Multiple (value/servicing fees)	2.90		2.73
Weighted-average note rate	4.76%		5.13%
Weighted-average age (in years)	4 years		4 years 2 months 12 days
Weighted-average expected prepayment (constant prepayment rate)	13.10%		13.20%
Weighted-average expected life (in years)	6 years 3 months 18 days		6 years 1 month 6 days
Weighted-average discount rate	12.00%		12.10%
Government [Member]
Servicing Assets at Fair Value [Line Items]
Servicing portfolio	41,192		39,048
Fair value	474		314
Value (bps)	115		80
Weighted-average servicing fees (bps)	32		33
Multiple (value/servicing fees)	3.59		2.42
Weighted-average note rate	4.26%		4.57%
Weighted-average age (in years)	2 years 6 months		2 years 4 months 24 days
Weighted-average expected prepayment (constant prepayment rate)	12.60%		21.20%
Weighted-average expected life (in years)	6 years 6 months		4 years 2 months 12 days
Weighted-average discount rate	11.20%		11.40%
Conventional [Member]
Servicing Assets at Fair Value [Line Items]
Servicing portfolio	170,447		162,446
Fair value	$ 1,932		$ 1,232
Value (bps)	113		76
Weighted-average servicing fees (bps)	29		30
Multiple (value/servicing fees)	3.90		2.53
Weighted-average note rate	4.19%		4.48%
Weighted-average age (in years)	2 years 4 months 24 days		2 years 6 months
Weighted-average expected prepayment (constant prepayment rate)	12.20%		20.40%
Weighted-average expected life (in years)	6 years 9 months 18 days		4 years 1 month 6 days
Weighted-average discount rate	9.80%		10.00%