Mortgage Servicing Rights - MSRs and Related Characteristics by Portfolio (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013 Y BasisPoint Multiple	Dec. 31, 2012 BasisPoint Y Multiple	Mar. 31, 2012	Dec. 31, 2011
Servicing Assets at Fair Value [Line Items]
Servicing portfolio	$ 220,321	$ 215,637
Fair value	1,955	1,700	1,737	1,519
Value (bps)	89	79
Weighted-average servicing fees (bps)	31	31
Multiple (value/servicing fees)	2.87	2.55
Weighted-average note rate	4.43%	4.54%
Weighted-average age (in years)	2.6	2.6
Weighted-average expected prepayment (constant prepayment rate)	17.00%	20.10%
Weighted-average expected life (in years)	4.9	4.2
Weighted-average discount rate	10.30%	10.40%
MRBP [Member]
Servicing Assets at Fair Value [Line Items]
Servicing portfolio	14,258	14,143
Fair value	151	154
Value (bps)	106	109
Weighted-average servicing fees (bps)	40	40
Multiple (value/servicing fees)	2.65	2.73
Weighted-average note rate	5.02%	5.13%
Weighted-average age (in years)	4.2	4.2
Weighted-average expected prepayment (constant prepayment rate)	12.80%	13.20%
Weighted-average expected life (in years)	6.1	6.1
Weighted-average discount rate	12.10%	12.10%
Government [Member]
Servicing Assets at Fair Value [Line Items]
Servicing portfolio	39,582	39,048
Fair value	343	314
Value (bps)	87	80
Weighted-average servicing fees (bps)	33	33
Multiple (value/servicing fees)	2.64	2.42
Weighted-average note rate	4.45%	4.57%
Weighted-average age (in years)	2.4	2.4
Weighted-average expected prepayment (constant prepayment rate)	19.10%	21.20%
Weighted-average expected life (in years)	4.6	4.2
Weighted-average discount rate	11.30%	11.40%
Conventional [Member]
Servicing Assets at Fair Value [Line Items]
Servicing portfolio	166,481	162,446
Fair value	$ 1,461	$ 1,232
Value (bps)	88	76
Weighted-average servicing fees (bps)	30	30
Multiple (value/servicing fees)	2.93	2.53
Weighted-average note rate	4.37%	4.48%
Weighted-average age (in years)	2.5	2.5
Weighted-average expected prepayment (constant prepayment rate)	16.90%	20.40%
Weighted-average expected life (in years)	4.9	4.1
Weighted-average discount rate	9.90%	10.00%