Mortgage Servicing Assets - Schedule of Range and Weighted-Average of Significant Unobservable Inputs (Detail) (Mortgage Servicing Assets [Member], Discounted Cash Flow [Member], USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Servicing Assets at Fair Value [Line Items]
Prepayment speed	4.90%	8.60%
Expected defaults	2.00%	2.30%
Residual cash flows discount rate	7.80%	8.90%
Escrow earn rate	1.80%	1.50%
Servicing cost	$ 963	$ 5,629
Loan assumption rate	1.58%	2.38%
Percentage late	0.33%	0.22%
Minimum [Member]
Servicing Assets at Fair Value [Line Items]
Prepayment speed	1.90%	0.00%
Expected defaults	1.00%	1.00%
Residual cash flows discount rate	7.00%	7.00%
Escrow earn rate	0.40%	0.20%
Servicing cost	150	924
Loan assumption rate	0.20%	0.00%
Percentage late	0.00%	0.00%
Maximum [Member]
Servicing Assets at Fair Value [Line Items]
Prepayment speed	11.30%	25.00%
Expected defaults	3.00%	3.00%
Residual cash flows discount rate	14.00%	15.00%
Escrow earn rate	3.10%	2.56%
Servicing cost	$ 2,600	$ 24,099
Loan assumption rate	3.00%	3.00%
Percentage late	2.00%	2.00%