MSRs and Related Characteristics by Portfolio (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012 BasisPoint Y Multiple		Jun. 30, 2012	Dec. 31, 2011 BasisPoint Multiple Y		Sep. 30, 2011	Jun. 30, 2011	Dec. 31, 2010
Servicing Assets at Fair Value [Line Items]
Servicing portfolio	$ 211,263			$ 191,082
Fair market value	1,553		1,594	1,519		1,466	1,989	1,837
Value (bps)	74	[1]		79	[1]
Weighted-average servicing fees (bps)	31			31
Multiple (value/servicing fees)	2.39			2.55
Weighted-average note rate	4.68%			5.03%
Weighted-average age (in years)	2.6			2.8
Weighted-average expected prepayment (constant prepayment rate)	22.20%			21.30%
Weighted-average expected life (in years)	3.8			4.0
Weighted-average discount rate	10.40%			10.40%
MRBP
Servicing Assets at Fair Value [Line Items]
Servicing portfolio	13,939			13,357
Fair market value	154			155
Value (bps)	110	[1]		116	[1]
Weighted-average servicing fees (bps)	40			40
Multiple (value/servicing fees)	2.75			2.90
Weighted-average note rate	5.24%			5.50%
Weighted-average age (in years)	4.2			4.2
Weighted-average expected prepayment (constant prepayment rate)	13.10%			12.90%
Weighted-average expected life (in years)	6.2			6.4
Weighted-average discount rate	12.10%			12.10%
Government
Servicing Assets at Fair Value [Line Items]
Servicing portfolio	38,162			32,567
Fair market value	304			290
Value (bps)	80	[1]		89	[1]
Weighted-average servicing fees (bps)	34			36
Multiple (value/servicing fees)	2.35			2.47
Weighted-average note rate	4.69%			5.08%
Weighted-average age (in years)	2.4			2.5
Weighted-average expected prepayment (constant prepayment rate)	21.60%			21.10%
Weighted-average expected life (in years)	4.0			4.0
Weighted-average discount rate	11.40%			11.30%
Conventional
Servicing Assets at Fair Value [Line Items]
Servicing portfolio	159,162	[2]		145,158	[2]
Fair market value	$ 1,095	[2]		$ 1,074	[2]
Value (bps)	69	[1],[2]		74	[1],[2]
Weighted-average servicing fees (bps)	30	[2]		29	[2]
Multiple (value/servicing fees)	2.30	[2]		2.55	[2]
Weighted-average note rate	4.63%	[2]		4.97%	[2]
Weighted-average age (in years)	2.5	[2]		2.8	[2]
Weighted-average expected prepayment (constant prepayment rate)	23.10%	[2]		22.10%	[2]
Weighted-average expected life (in years)	3.5	[2]		3.8	[2]
Weighted-average discount rate	10.00%	[2]		10.00%	[2]

[1] Value is calculated as fair market value divided by the servicing portfolio.

[2] Represents loans sold primarily to GSEs.