Mortgage Servicing Rights - Sensitivity to Changes in Interest Rates of the Fair Value of MSRs Portfolio and Related Derivative Instruments (Detail) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Down Scenario [Member] | Mortgage Servicing Rights [Member]
Sensitivity Analysis of Fair Value of Interests Continued to be Held by Transferor, Servicing Assets or Liabilities, Impact of Adverse Change in Assumption [Line Items]
Net fair value 100 basis points	$ (475)	$ (476)
Net fair value 50 basis points	(210)	(209)
Net fair value 25 basis points	(99)	(98)
Down Scenario [Member] | Derivative [Member]
Sensitivity Analysis of Fair Value of Interests Continued to be Held by Transferor, Servicing Assets or Liabilities, Impact of Adverse Change in Assumption [Line Items]
Net fair value 100 basis points	418	375
Net fair value 50 basis points	201	180
Net fair value 25 basis points	98	88
Down Scenario [Member] | Net Sensitivity [Member]
Sensitivity Analysis of Fair Value of Interests Continued to be Held by Transferor, Servicing Assets or Liabilities, Impact of Adverse Change in Assumption [Line Items]
Net fair value 100 basis points	(57)	(101)
Net fair value 50 basis points	(9)	(29)
Net fair value 25 basis points	(1)	(10)
Up Scenario [Member] | Mortgage Servicing Rights [Member]
Sensitivity Analysis of Fair Value of Interests Continued to be Held by Transferor, Servicing Assets or Liabilities, Impact of Adverse Change in Assumption [Line Items]
Net fair value 100 basis points	269	270
Net fair value 50 basis points	159	159
Net fair value 25 basis points	86	85
Up Scenario [Member] | Derivative [Member]
Sensitivity Analysis of Fair Value of Interests Continued to be Held by Transferor, Servicing Assets or Liabilities, Impact of Adverse Change in Assumption [Line Items]
Net fair value 100 basis points	(325)	(314)
Net fair value 50 basis points	(175)	(165)
Net fair value 25 basis points	(91)	(84)
Up Scenario [Member] | Net Sensitivity [Member]
Sensitivity Analysis of Fair Value of Interests Continued to be Held by Transferor, Servicing Assets or Liabilities, Impact of Adverse Change in Assumption [Line Items]
Net fair value 100 basis points	(56)	(44)
Net fair value 50 basis points	(16)	(6)
Net fair value 25 basis points	$ (5)	$ 1