Mortgage Servicing Assets - Schedule of Range and Weighted-Average of Significant Unobservable Inputs (Detail) - Discounted Cash Flow [Member] - USD ($)	6 Months Ended		12 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Weighted Average [Member]
Servicing Assets at Fair Value [Line Items]
Prepayment speed	4.20%	4.70%	4.60%
Expected defaults	1.60%	1.80%	1.70%
Residual cash flows discount rate	7.90%	7.80%	7.80%
Escrow earn rate	2.10%	2.00%	2.30%
Servicing cost	$ 1,136,000,000	$ 1,088,000,000	$ 1,215,000,000
Loan assumption rate	1.27%	1.41%	1.34%
Percentage late	0.34%	0.32%	0.33%
Minimum [Member]
Servicing Assets at Fair Value [Line Items]
Prepayment speed	1.50%	1.70%	1.90%
Expected defaults	1.00%	1.00%	1.00%
Residual cash flows discount rate	7.00%	7.00%	7.00%
Escrow earn rate	0.90%	0.70%	1.00%
Servicing cost	$ 150,000,000	$ 150,000,000	$ 150,000,000
Loan assumption rate	0.00%	0.20%	0.00%
Percentage late	0.00%	0.00%	0.00%
Maximum [Member]
Servicing Assets at Fair Value [Line Items]
Prepayment speed	17.50%	14.90%	17.20%
Expected defaults	3.00%	3.00%	3.00%
Residual cash flows discount rate	15.00%	15.00%	15.00%
Escrow earn rate	3.00%	3.30%	3.50%
Servicing cost	$ 2,700,000,000	$ 2,750,000,000	$ 2,700,000,000
Loan assumption rate	3.00%	3.00%	3.00%
Percentage late	2.10%	2.00%	2.00%